I am having a problem with our approach to data persistence in our app. It was decided to use NSUserDefaults with NSCoding compliant data model, which I disagree with due to the scale of our app.
The problem I'm seeing is when the data model changes, any attempt to deserialized results in a crash. The app must be uninstalled and reinstalled in order to re-serialize.
Scenario:
User installs app
User does stuff.
Developer decides that a property should be added to one of the serialized objects and pushes an update.
User installs update.
App goes 'kaboom'.
This is happening because the data had been serialized with a different model than it is now attempting to be deserialized as.
Example:
class Contact: NSCoding {
var name
var address
var userId
}
... // NSCoding compliance happens next. This object gets serialized.
Someone decides that Contact needs more stuff:
class Contact: NSCoding {
var name
var address
var userId
var phoneNumber
var emailAddress
}
Attempting to deserialize the Contact object, even though the NSCoding compliance for encoding and decoding has been updated to load and deserialize, causes
fatal error: unexpectedly found nil while unwrapping an Optional value
CoreDataManager.unarchiveUser
Worker.init
So, my question is, how could we possibly avoid this crash from occurring when running an updated version of the app that has a different schema??
You're crashing because,
You are attempting to decodeObject(forKey:) on a key that doesn't exist (because it didn't exist on the class when the object was encoded). This method returns nil.
You are using ! to force-unwrap the result of #1.
As a rule of thumb, if your Swift code crashes on a line that contains a !, there's about a 95% chance that the ! is the direct cause of the crash. If the error message mentions unwrapping an optional, it's a 100% chance.
The documentation for the decodeObject(forKey:) method explains that it may return nil. In your case this is guaranteed to happen if you're upgrading from a previous version of the class and you're decoding a key that you just added.
Your code needs to recognize that there might not be a value for the new properties. The simplest fix is replacing as! with as?. Then you'll get a nil value for the new property. For properties that are not optional, you can add something like ?? "default value" to the end.
You could also use the containsValue(forKey:) method to check if a value exists before trying to decode the key.
Related
I've been working on cross contract calls and simulation testing. I gnereally have things working when I use function calls but I'm seeing a wasm execution error "HostError(ProhibitedInView { method_name: "promise_batch_create") when trying to use a 'view' to call a method that generates a cross contract call to get its information.
contract1 has a method (indirect_num_entries) that uses a cross contract call to a method (num_entries) in contract2 that returns acount (with no modifications)
const contract1 = new nearAPI.Contract(
account1, // the account object that is connecting
"example-contract.testnet",
{
// name of contract you're connecting to
viewMethods: ["indirect_num_entries"], // view methods do not change state but usually return a value
changeMethods: ["indirect_add_entry"], // change methods modify state
sender: account, // account object to initialize and sign transactions.
}
);
and for contract2
const contract2 = new nearAPI.Contract(
account2, // the account object that is connecting
"example-contract.testnet",
{
// name of contract you're connecting to
viewMethods: ["num_entries"], // view methods do not change state but usually return a value
changeMethods: ["add_entry"], // change methods modify state
sender: account, // account object to initialize and sign transactions.
}
);
All of that works correctly via the Javascript SDK for both adding and getting the number of entries.
However I ran into a problem while trying to create a simulation test and found that trying to use view on indirect_num_entries caused an error:
let x : u64 = view!(contract1.indirect_num_entries()).unwrap_json(); //error
caused the following runtime error:
An error occurred
Error: Querying [object Object] failed: wasm execution failed with error: FunctionCallError(HostError(ProhibitedInView { method_name: "promise_batch_create" })).
Playing around a bit I found that replacing the view! with a call! worked -- i.e.
let x : u64 = call!(root, contract1.indirect_num_entries()).unwrap_json(); // works
I also found that if I use the near-cli I see the same behavior i.e.
near call contract1 indirect_num_entries "{}" --accountI contract1 (works)
near view contract1 indirect_num_entries (errors)
whereas for views directly to the contract2 work just fine
near view contract2 num_entries (works)
let x : u64 = view!(contract2.num_entries()).unwrap_json(); // works
Is this as expected and view is only valid for methods that access (not modify) the local contract data and shouldn't be used for methods that issue a cross contract call? (Or am I doing something incorrectly?)
I can certainly imagine that there could be reasons for needing to use a call (e.g. perhaps the request for a cross contract call needs to be signed) but I don't recall anything/haven't found anything that seems to describes this. Is there a description or a explanation somewhere?
Thanks!
This article explains the issue
https://docs.near.org/docs/develop/contracts/as/intro#view-and-change-functions
view calls do not provide the same context as a change call
the reason is because view calls are unsigned. no sender has signed a transaction to make the call. this is useful, not requiring a signature, because some use cases are intended for casual browsing or frequent reading of data like browsing an NFT collection or rendering a dashboard
change calls require a signed transaction so they include context like sender and other details
cross-contract calls require gas and this gas should be charged to some account. without a signed transaction (in a view call) then there is no one to charge for this gas
this might make you wonder: "but don't view calls cost gas too?" ... yes, they do, and today the RPC node providers are subsidizing these calls but that may change in the future
The Q&A is currently a subject of meta discussion, do participate. The current plan is to split where possible into Q&As. Answers to the A&A are community wiki and the question should become one when the status is resolved.
Preface
This Q&A strives to become a collection and a reference target for common errors encountered during development in Google Apps Script language in hopes to improve long-term maintainability of google-apps-script tag.
There are several similar and successful undergoings in other languages and general-purpose tags (see c++, android, php, php again), and this one follows suit.
Why it exists?
The amount of questions from both new and experienced developers regarding the meaning and solutions to errors encountered during development and production that can be effectively reduced to a single answer is substantial. At the time of writing, even running a query only by language tag yields:
"Cannot find method" 8 pages
"Cannot read property" 9 pages
"Cannot call ... in this context" 5 pages
"You do not have permission" 11 pages
Linking to a most relevant duplicate is hard and time-consuming for volunteers due to the need to consider nuances and often poorly-worded titles.
What it consists of?
Entries in this Q&A contain are designed to provide info on how to:
parse the error message structure
understand what the error entails
consistently reproduce (where applicable)
resolve the issue
provide a link to canonical Q&A (where possible)
Table of Contents
To help you navigate the growing reference please use the TOC below:
General errors
Service-specific errors
What this is not?
The scope of the Q&A is limited to common (not trivial). This is not:
a catch-all guide or "best practices" collection
a reference for general ECMAScript errors
GAS documentation
a resources list (we have a tag wiki for that)
What to add?
When adding an entry, please, consider the following:
is the error common enough (see "why" section for examples)?
can the solution be described concisely and be applicable for most cases?
Preface
The answer provides a guide on general errors that can be encountered when working with any Google service (both built-in and advanced) or API. For errors specific to certain services, see the other answer.
Back to reference
General errors
Message
TypeError: Cannot read property 'property name here' from undefined (or null)
Description
The error message indicates that you are trying to access a property on an Object instance, but during runtime the value actually held by a variable is a special data type undefined. Typically, the error occurs when accessing nested properties of an object.
A variation of this error with a numeric value in place of property name indicates that an instance of Array was expected. As arrays in JavaScript are objects, everything mentioned here is true about them as well.
There is a special case of dynamically constructed objects such as event objects that are only available in specific contexts like making an HTTP request to the app or invoking a function via time or event-based trigger.
The error is a TypeError because an "object" is expected, but "undefined" is received
How to fix
Using default values
Logical OR || operator in JavaScript has an intersting property of evaluating the right-hand side iff the left-hand is falsy. Since objects in JS are truthy, and undefined and null are falsy, an expression like (myVar || {}).myProp [(myVar || [])[index] for arrays] will guarantee that no error is thrown and the property is at least undefined.
One can also provide default values: (myVar || { myProp : 2 }) guarantees accessing myProp to return 2 by default. Same goes for arrays: (myVar || [1,2,3]).
Checking for type
Especially true for the special case, typeof operator combined with an if statement and a comparison operator will either allow a function to run outside of its designated context (i.e. for debugging purposes) or introduce branching logic depending on whether the object is present or not.
One can control how strict the check should be:
lax ("not undefined"): if(typeof myVar !== "undefined") { //do something; }
strict ("proper objects only"): if(typeof myVar === "object" && myVar) { //do stuff }
Related Q&As
Parsing order of the GAS project as the source of the issue
Message
Cannot convert some value to data type
Description
The error is thrown due to passing an argument of different type than a method expects. A common mistake that causes the error is accidental coercion of a number to string.
How to reproduce
function testConversionError() {
const ss = SpreadsheetApp.getActiveSheet();
ss.getRange("42.0",1);
}
How to fix
Make sure that the value referenced in the error message is of data type required by documentation and convert as needed.
Message
Cannot call Service and method name from this context
Description
This error happens on a context mismatch and is specific to container-bound scripts.
The primary use case that results in the error is trying to call a method only available in one document type (usually, getUi() as it is shared by several services) from another (i.e. DocumentApp.getUi() from a spreadsheet).
A secondary, but also prominent case is a result of calling a service not explicitly allowed to be called from a custom function (usually a function marked by special JSDoc-style comment #customfunction and used as a formula).
How to reproduce
For bound script context mismatch, declare and run this function in a script project tied to Google Sheets (or anything other than Google Docs):
function testContextMismatch() {
const doc = DocumentApp.getUi();
}
Note that calling a DocumentApp.getActiveDocument() will simply result in null on mismatch, and the execution will succeed.
For custom functions, use the function declared below in any cell as a formula:
/**
* #customfunction
*/
function testConversionError() {
const ui = SpreadsheetApp.getUi();
ui.alert(`UI is out of scope of custom function`);
}
How to fix
Context mismatch is easily fixed by changing the service on which the method is called.
Custom functions cannot be made to call these services, use custom menus or dialogs.
Message
Cannot find method Method name here
The parameters param names do not match the method signature for method name
Description
This error has a notoriously confusing message for newcomers. What it says is that a type mismatch occurred in one or more of the arguments passed when the method in question was called.
There is no method with the signature that corresponds to how you called it, hence "not found"
How to fix
The only fix here is to read the documentation carefully and check if order and inferred type of parameters are correct (using a good IDE with autocomplete will help). Sometimes, though, the issue happens because one expects the value to be of a certain type while at runtime it is of another. There are several tips for preventing such issues:
Setting up type guards (typeof myVar === "string" and similar).
Adding a validator to fix the type dynamically thanks to JavaScript being dynamically typed.
Sample
/**
* #summary pure arg validator boilerplate
* #param {function (any) : any}
* #param {...any} args
* #returns {any[]}
*/
const validate = (guard, ...args) => args.map(guard);
const functionWithValidator = (...args) => {
const guard = (arg) => typeof arg !== "number" ? parseInt(arg) : arg;
const [a,b,c] = validate(guard, ...args);
const asObject = { a, b, c };
console.log(asObject);
return asObject;
};
//driver IIFE
(() => {
functionWithValidator("1 apple",2,"0x5");
})()
Messages
You do not have permission to perform that action
The script does not have permission to perform that action
Description
The error indicates that one of the APIs or services accessed lacks sufficient permissions from the user. Every service method that has an authorization section in its documentation requires at least one of the scopes to be authorized.
As GAS essentially wraps around Google APIs for development convenience, most of the scopes listed in OAuth 2.0 scopes for APIs reference can be used, although if one is listed in the corresponding docs it may be better to use it as there are some inconsistencies.
Note that custom functions run without authorization. Calling a function from a Google sheet cell is the most common cause of this error.
How to fix
If a function calling the service is ran from the script editor, you are automatically prompted to authorize it with relevant scopes. Albeit useful for quick manual tests, it is best practice to set scopes explicitly in application manifest (appscript.json). Besides, automatic scopes are usually too broad to pass the review if one intends to publish the app.
The field oauthScopes in manifest file (View -> Show manifest file if in code editor) should look something like this:
"oauthScopes": [
"https://www.googleapis.com/auth/script.container.ui",
"https://www.googleapis.com/auth/userinfo.email",
//etc
]
For custom functions, you can fix it by switching to calling the function from a menu or a button as custom functions cannot be authorized.
For those developing editor Add-ons, this error means an unhandled authorization lifecycle mode: one has to abort before calls to services that require authorization in case auth mode is AuthMode.NONE.
Related causes and solutions
#OnlyCurrentDoc limiting script access scope
Scopes autodetection
Message
ReferenceError: service name is not defined
Description
The most common cause is using an advanced service without enabling it. When such a service is enabled, a variable under the specified identifier is attached to global scope that the developer can reference directly. Thus, when a disabled service is referenced, a ReferenceError is thrown.
How to fix
Go to "Resources -> Advanced Google Services" menu and enable the service referenced. Note that the identifier should equal the global variable referenced.
For a more detailed explanation, read the official guide.
If one hasn't referenced any advanced services then the error points to an undeclared variable being referenced.
Message
The script completed but did not return anything.
Script function not found: doGet or doPost
Description
This is not an error per se (as the HTTP response code returned is 200 and the execution is marked as successful, but is commonly regarded as one. The message appears when trying to make a request/access from browser a script deployed as a Web App.
There are two primary reasons why this would happen:
There is no doGet or doPost trigger function
Triggers above do not return an HtmlOutput or TextOutput instance
How to fix
For the first reason, simply provide a doGet or doPost trigger (or both) function. For the second, make sure that all routes of your app end with creation of TextOutput or HtmlOutput:
//doGet returning HTML
function doGet(e) {
return HtmlService.createHtmlOutput("<p>Some text</p>");
}
//doPost returning text
function doPost(e) {
const { parameters } = e;
const echoed = JSON.stringify(parameters);
return ContentService.createTextOutput(echoed);
}
Note that there should be only one trigger function declared - treat them as entry points to your application.
If the trigger relies on parameter / parameters to route responses, make sure that the request URL is structured as "baseURL/exec?query" or "baseURL/dev?query" where query contains parameters to pass.
Related Q&As
Redeploying after declaring triggers
Message
We're sorry, a server error occurred. Please wait a bit and try again.
Description
This one is the most cryptic error and can occur at any point with nearly any service (although DriveApp usage is particularly susceptible to it). The error usually indicates a problem on Google's side that either goes away in a couple of hours/days or gets fixed in the process.
How to fix
There is no silver bullet for that one and usually, there is nothing you can do apart from filing an issue on the issue tracker or contacting support if you have a GSuite account. Before doing that one can try the following common remedies:
For bound scripts - creating a new document and copying over the existing project and data.
Switch to using an advanced Drive service (always remember to enable it first).
There might be a problem with a regular expression if the error points to a line with one.
Don't bash your head against this error - try locating affected code, file or star an issue and move on
Syntax error without apparent issues
This error is likely to be caused by using an ES6 syntax (for example, arrow functions) while using the deprecated Rhino runtime (at the time of writing the GAS platform uses V8).
How to fix
Open "appscript.json" manifest file and check if runtimeVersion is set to "V8", change it if not, or remove any ES6 features otherwise.
Quota-related errors
There are several errors related to quotas imposed on service usage. Google has a comprehensive list of those, but as a general rule of thumb, if a message matches "too many" pattern, you are likely to have exceeded the respective quota.
Most likely errors encountered:
Service invoked too many times: service name
There are too many scripts running
Service using too much computer time for one day
This script has too many triggers
How to fix
In most cases, the only fix is to wait until the quota is refreshed or switch to another account (unless the script is deployed as a Web App with permission to "run as me", in which case owner's quotas will be shared across all users).
To quote documentation at the time:
Daily quotas are refreshed at the end of a 24-hour window; the exact time of this refresh, however, varies between users.
Note that some services such as MailApp have methods like getRemainingDailyQuota that can check the remaining quota.
In the case of exceeding the maximum number of triggers one can check how many are installed via getProjectTriggers() (or check "My triggers" tab) and act accordingly to reduce the number (for example, by using deleteTrigger(trigger) to get rid of some).
Related canonical Q&As
How are daily limitations being applied and refreshed?
"Maximum execution time exceeded" problem
Optimizing service calls to reduce execution time
References
How to make error messages more meaningful
Debugging custom functions
Service-specific errors
The answer concerns built-in service-related errors. For general reference see the other answer. Entries addressing issues with services listed in official reference are welcome.
Back to reference
SpreadsheetApp
The number of rows in the range must be at least 1
This error is usually caused by calling the getRange method where the parameter that sets the number of rows happens to equal to 0. Be careful if you depend on getLastRow() call return value - only use it on non-empty sheets (getDataRange will be safer).
How to reproduce
sh.getRange(1, 1, 0, sh.getLastColumn()); //third param is the number of rows
How to fix
Adding a guard that prevents the value from ever becoming 0 should suffice. The pattern below defaults to the last row with data (optional if you only need a certain number of rows) and to 1 if that also fails:
//willFail is defined elsewhere
sh.getRange(1, 1, willFail || sh.getLastRow() || 1, sh.getLastColumn());
Error: “Reference does not exist”
The error happens when calling a custom function in a spreadsheet cell that does not return a value. The docs do mention only that one "must return a value to display", but the catch here is that an empty array is also not a valid return value (no elements to display).
How to reproduce
Call the custom function below in any Google Sheets spreadsheet cell:
/**
* #customfunction
*/
const testReferenceError = () => [];
How to fix
No specific handling is required, just make sure that length > 0.
The number of rows or cells in the data does not match the number of rows or cells in the range. The data has N but the range has M.
Description
The error points to a mismatch in dimensions of range in relation to values. Usually, the issue arises when using setValues() method when the matrix of values is smaller or bigger than the range.
How to reproduce
function testOutOfRange() {
const ss = SpreadsheetApp.getActiveSpreadsheet();
const sh = ss.getActiveSheet();
const rng = sh.getActiveRange();
const vals = rng.getValues();
try {
vals.push([]);
rng.setValues(vals);
} catch (error) {
const ui = SpreadsheetApp.getUi();
ui.alert(error.message);
}
}
How to fix
If it is routinely expected for values to get out of bounds, implement a guard that catches such states, for example:
const checkBounds = (rng, values) => {
const targetRows = rng.getHeight();
const targetCols = rng.getWidth();
const { length } = values;
const [firstRow] = values;
return length === targetRows &&
firstRow.length === targetCols;
};
The coordinates of the range are outside the dimensions of the sheet.
Description
The error is a result of a collision between two issues:
The Range is out of bounds (getRange() does not throw on requesting a non-existent range)
Trying to call a method on a Range instance referring to a non-existent dimension of the sheet.
How to reproduce
function testOB() {
const ss = SpreadsheetApp.getActiveSpreadsheet();
const sh = ss.getActiveSheet();
const rng = sh.getRange(sh.getMaxRows() + 1, 1);
rng.insertCheckboxes();
}
How to fix
Check that number of rows (getMaxRow()) and columns (getMaxColumns()) are both greater or equal to the parameters passed to getRange() method call and change them accordingly.
Exception: You can't create a filter in a sheet that already has a filter.
Description
The message means that you are trying to call a createFilter method on a Range in a Sheet that already has a filter set (either via UI or script), thus violating the restriction on 1 filter per Sheet, to quote the documentation:
There can be at most one filter in a sheet.
How to reproduce
const testFilterExistsError = () => {
const sh = SpreadsheetApp.getActiveSheet();
const rng = sh.getDataRange();
const filter1 = rng.createFilter();
const filter2 = rng.createFilter();
};
How to fix
Add a guard that checks for the existence of the filter first. getFilter returns either a filter or null if called on a Range instance and is perfect for the job:
const testFilterGuard = () => {
const sh = SpreadsheetApp.getActiveSheet();
const rng = sh.getDataRange();
const filter = rng.getFilter() || rng.createFilter();
//do something useful;
};
UrlFetchApp
Attribute provided with no value: url
Description
The error is specific to UrlFetchApp service and happens when fetch or fetchAll method gets called with an empty string or non-string value.
How to reproduce
const response = UrlFetchApp.fetch("", {});
How to fix
Make sure that a string containing a URI (not necessarily valid) is passed to the method as its first argument. As its common root cause is accessing a non-existent property on an object or array, check whether your accessors return an actual value.
I have a SecTrustRef object from the system that I'd like to evaluate myself. Just calling SecTrustEvaluateAsync will be sufficient for this job. The problem is, I must evaluate it in a different process as only this other process has access to the keychains where the CA certificates are stored that may cause evaluation to succeed.
The two processes have an IPC link that allows me to exchange arbitrary byte data between them but I don't see any way to easily serialize a SecTrustRef into byte data and deserialize that data back to an object at the other process. There doesn't seem to be a persistent storage mechanism for SecTrustRef.
So am I overlooking something important here, or do I really have to get all the certs (SecTrustGetCertificateAtIndex) and all the policies (SecTrustCopyPolicies) and serialize these myself?
And if so, how would I serialize a policy?
For the certificate (SecCertificateRef) it's rather easy, I just call SecCertificateCopyData and later on SecCertificateCreateWithData.
But for policies I can only call SecPolicyCopyProperties on one side and later on SecPolicyCreateWithProperties, however the later one requires a 2nd parameter, a policyIdentifier and I see no way to get that value from an existing policy. What am I missing?
Reading through the source of the Security framework, I finally figured it out how to copy a SecPolicyRef:
SecPolicyCreateWithProperties wants what it calls a "policyIdentifier". It's a constant like kSecPolicyAppleIPsec.
This does not get stored directly by the function, it's comparing the value and calling dedicated internal "initializers" (like SecPolicyCreateIPsec).
These in turn call SecPolicyCreate (which is private). They end up passing the same identifier value that you passed to SecPolicyCreateWithProperties.
And this value then gets stored as-is in the _oid field!
The identifier is actually the OID. You can get it either via SecPolicyCopyProperties(policy) (stored in the dictionary with key kSecPolicyOid) or via SecPolicyGetOID (but that returns it as an inconvenient CSSM_OID). Some of those specialized initializers also use values from the properties dictionary passed to SecPolicyCreateWithProperties, those should be present in the copied properties dictionary already.
So this gives us:
Serialization:
CFDictionaryRef createSerializedPolicy(SecPolicyRef policy) {
// Already contains all the information needed.
return SecPolicyCopyProperties(policy);
}
Deserialization:
SecPolicyRef createDeserializedPolicy (CFDictionaryRef serialized) {
CFStringRef oid = CFDictionaryGetValue(serialized, kSecPolicyOid);
if (oid == NULL || CFGetTypeID(oid) != CFStringGetTypeID()) {
return NULL;
}
return SecPolicyCreateWithProperties(oid, serialized);
}
To reproduce the original SecTrustRef as closely as possible, the anchors need to be copied as well. There is an internal variable _anchorsOnly which is set to true once you set anchors. Unfortunately, there is no way to query this value and I've seen it being false in trusts passed by NSURLSession, for example. No idea yet on how to get this value in a public way.
Another problematic bit are the exceptions: if _exceptions is NULL but you query them via SecTrustCopyExceptions(trust), you do get data! And if you assign that to the deserialized trust via SecTrustSetExceptions(trust, exceptions) you suddenly end up with exceptions that were not there before and can change the evaluation result! (I've seen those suddenly appearing exceptions lead to an evaluation result of "proceed" instead of "recoverable trust failure").
When I save a change to the ACL on a PFObject (in this case, making it publicly writeable), the completion block runs successfully but the change is not actually saved to the server. Re-fetching the object, or viewing it via Parse Dashboard, shows that the ACL change is not persisted. In fact, I have verified via server logging that Parse server never even receives a request.
// first fetch an object from the parse server, then...
print("before: \(object.acl?.hasPublicWriteAccess)") // "false"
object.acl?.hasPublicWriteAccess = true
object.saveInBackground { (success, error) in
// confirm that success is true and error is nil
print("after: \(object.acl?.hasPublicWriteAccess)") // "true" - object is updated client-side
// now, re-fetch the same object or check it in Parse Dashboard. It is not saved as publicly editable.
}
When changing an object's ACL, the object itself is not marked as 'dirty', so saving it does not result in a request to the server. You can verify this by checking the isDirty property on the object after changing the ACL.
This is in common with other PFObjects - a change to a pointer property does not mark the parent object as dirty. This is not normally encountered since it is natural to simply save the pointer object itself. Since there is no PFACL.save() function, we can instead re-set the acl property on the object to ensure that it is marked as dirty:
object.acl?.hasPublicWriteAccess = toggle.isOn
object.acl = object.acl
object.saveEventually()
Additional discussion of this can be found in this issue.
Someone doesn't understand what i want. I want to know what i can do with a pointer.
I have js cloud code.
I have a pointer.
What can i do with it?
Example:
var query = new Parse.Query("Messages"); //POINTER QUERY
console.log(userMessages[0].get("messageId"));
console.log("end2");
query.equalTo("objectId",userMessages[position].get("messageId"));
In the example, userMessages is the result of a prior cloud query.
This line
console.log(userMessages[0].get("messageId"));
helpfully outputs
{"__type":"Pointer","className":"Messages","objectId":"5J4eOletgz"}
This is less useful than you might imagine. I cannot seem to call the objectId from it, and the query
query.equalTo("objectId",userMessages[position].get("messageId"));
query.find ({ ... });
returns nothing. Note that the query should find the pointer-object the pointer-points-to, but instead it helpfully throws the error
Error: 102 bad special key: __type
Which is just about useless.
What can i do with a pointer?
Why don't the people at parse.com bother to write this stuff up anywhere?
That second question is more like a buddhist koan for them to meditate over, no need to respond!
you can use:
userMessagesQuery.include("messageId")
before you execute your query that returns userMessages and you will get the entire object in "messageId" instead of just a pointer.
Also you use
userMessages[0].get("messageId").fetch({success:function(){}})
to get the full object if you don't want to use "include"
Suggestion: I'd rename "messageId" to "message" to make it clear that it's an object pointer and not an ID field.
A pointer is a Parse object with just the minimal data used for linking. If you want to get the rest of the data for a pointer (fully populate it), use the fetch() method.
If you just want the objectId from a pointer, you retrieve it just like you would any other Parse object, by using the myPointer.objectId property.
In your case the following would work, but isn't the most optimal solution:
// I would suggest renaming messageId if you're actually storing pointers
var messagePointer = userMessages[position].get("messageId");
query.equalTo("objectId", messagePointer.objectId);
Instead, as stated by #RipRyness, you could just change your previous query to include() the full object, avoiding many extra queries.
userMessagesQuery.include("messageId");
// ... later in success handler ...
// now a fully populated Message object
var message = userMessages[position].get("messageId");
console.log(message);
Okay so a pointer is does not only point to a certain object, but it can BE that object.
In the query that returns the userMessages result, you can use the line .include("messageId") - this makes your query not only return a pointer to that object, it actually includes that object in place of the pointer.
After using the include statement, userMessages[0].get("messageId") will return the Message object linked that that userMessage object. You no longer need to query the Message collection to get the object.