I am having problem understanding prototypes in js and can't find an answer to what is happening.
function Person() { } //constructor to create empty Person obj
//confusion starts below, when adding same property to the same prototype obj but in 2 different ways, it gives me 2 difference behaviours and I don't know why, what the difference in these 2 statements is (I thought they do exact same thing, which they are but then both act differently with instances of the Person after)
Person.prototype = { age : 22 } //only new instances of the obj get this new value
Person.prototype.age = 44; //all instances new or old get the new value automatically
Related
hope you are doing well.
I have some list of other object which again contains two different objects. I have tried couple of ways using Collectors.groupingBy() but didn't get expected output. So help me to figure out solution to this.
Suppose I following three entities:
class FruitFlower {
Fruit fruit;
Flower flower;
}
class Fruit {
String name;
}
class Flower {
String name;
}
And I have a list like this
List<FruitFlower> fruitFlowers = new ArrayList<>();
fruitFlowers.addAll(
new FruitFlower(
new Fruit("Apple"),
new Flower("Rose")
),
new FruitFlower(
new Fruit("Banana"),
new Flower("Lily")
),
new FruitFlower(
new Fruit("Apple"),
new Flower("Sunflower")
),
new FruitFlower(
new Fruit("Banana"),
new Flower("Purple")
),
new FruitFlower(
new Fruit("Banana"),
new Flower("Rose")
)
);
Now, I want to order this list by some filter such that it returns HashMap like this
HashMap<Fruit,List<Flower>> hashMap=new HashMap<>();
Resultant Object:
{
"Apple":["Rose","Sunflower"]
"Banana":["Lily","Purple","Rose"]
}
Where
Expected output is a HadhMap that contains only unique values and a list of other values connected to that particular object. You can consider Objects of String for simplicity.
This is Java question and expected answer should be in Java 8 using stream API.
Thank you in advance.
As you suspected, groupingBy is the right approach.
fruitFlowers.stream().collect(Collectors.groupingBy(
i -> i.fruit,
Collectors.mapping(i -> i.flower, Collectors.toList())
));
The first parameter to groupingBy defines how you want to group them. In this case, we want to group by fruits.
The second parameter describes what the value of the resulting map should be. In this case, we want the values to be the list of flowers.
Note that this approach only works if groupingBy can deduce that two fruits are equivalent. This requires that the Fruit class contains an appropriate implementation of equals and hashCode.
If the Fruit class cannot be extended to add those methods, one can change the first lambda to i -> i.fruit.name, but that would make the resulting Map to have String keys instead of Fruit.
I have three entities generated by Entity Framework. One is event and this contains navigation properties called frogs and user_bookings. I posted a related question before about performing a sub-query which seems to work but it prevents me overriding lazy loading of a property.
var evts = from evt in context.events.Include("frogs")
where evt.event_id < 10
select evt;
This works - the navigation property frogs gets loaded.
However, when I alter the LINQ to this:
var evts = from evt in context.events.Include("frogs")
where evt.event_id < 10
select new
{
Event = evt,
HasBooked = evt.user_bookings.Any(x => x.user_id == 1)
};
I get an error trying to access the frogs because the ObjectContext no longer exists. I tried removing virtual from the class definition for the event class, but this just results in an empty list of frogs, when they are definitely there!
This is by design. Include is ignored when the query result is a projection, even when the projection contains an entity that could contain the Included properties.
I don't know why EF implemented it this way. If the projection doesn't contain any entities, but is just some type (anonymous or not), there is no Include target, so ignoring it makes sense. But if the projection does contain an Include target (Event in your case) it seems to me that they could have decided to make that work. But, well, they didn't.
Maybe it's because the rules when Include actually has an effect are less obvious than you might expect. In your case, the shape of the query changes after the Include, so it's ignored.
You could work around this by also querying the frogs:
from evt in context.events.Include("frogs")
where evt.event_id < 10
select new
{
Event = evt,
Frogs = evt.frogs,
HasBooked = evt.user_bookings.Any(x => x.user_id == 1)
};
Now each Event will also have its frogs collection filled (because of relationship fixup). But there are two gotchas. The collections are not marked as loaded, so -
if lazy load can occur afterwards, it will occur, making the initial load useless.
if lazy loading can't occur any more (because the context is disposed) you will get an exception.
This means that to make this work you have to disable lazy loading.
I want to add some calculated properties to an EntityObject without loosing the possibility of querying it agains the database.
I created a partial class and added the fields I need in the object. Than I wrote a static function "AttachProperties" that should somehow add some calculated values. I cannot do this on clientside, since several other functions attach some filter-conditions to the query.
The functions should look like this:
return query.Select(o =>
{
o.HasCalculatedProperties = true;
o.Value = 2;
return o;
});
In my case the calculated value depends on several lookups and is not just a simple "2". This sample works with an IEnumerable but, of course, not with an IQueryable
I first created a new class with the EntityObject as property and added the other necessary fields but now I need this extended class to be of the same basetype.
First, in my opinion changing objects in a Select() is a bad idea, because it makes something else happen (state change) than the method name suggests (projection), which is always a recipe for trouble. Linq is rooted in a functional programming (stateless) paradigm, so this kind of usage is just not expected.
But you can extend your class with methods that return a calculation result, like:
partial class EntityObject
{
public int GetValue()
{
return this.MappedProp1 * this.MappedProp2;
}
}
It is a bit hard to tell from your question whether this will work for you. If generating a calculated value involves more than a simple calculation from an object's own properties it may be better to leave your entities alone and create a services that return calculation results from an object graph.
Try something like this:
return from o in collection
select new O()
{
OtherProperty = o.OtherProperty,
HasCalculatedProperties = true,
Value = 2
};
This will create a copy of the original object with the changes you require and avoid all the messiness that come with modifying an entity in a select clause.
Hi I been searching for my error but I can't find anything that help me. The problem is this. I been working with Subsonic 3, Newtonsoft Json and the linq way of write so I have this easy query:
var found = from client in newclients.All() where client.Period == "sometext" select client;
string periodoJSON = JsonConvert.SerializeObject(periodoFound); //this get "Self referencing loop Exception"
the problem is when I run this script I get the horrible exception "Self referening loop exception" in the JsonConvert line, subsonic have all the objects without any problem but if I do the following.
var found = from client in newclients.All() where client.Period == "sometext" select new client{client.Name, client.LastName, etc};
string periodoJSON = JsonConvert.SerializeObject(periodoFound);
I get the object serialize with a any problem with all the properties. I'm doing the last way because I have to finish my work but is any other way or solution for this problem, if not I will have to write all the properties every time I want to get a full table properties.
hope any can solve my problem o help me in the path for find a solution....
what I have is a really basic query with linq and I try the three values for JsonSerializerSettings and any work, again I'm working with subsonic 3 this not happend either with subsnoic 2 and I can make it work if I specify one by one the properties of the object in the linq query does any have any clue of what is happend, ANY more help would be great!!! If I put the value of Serialize my page get crazy and in a infinity loop state, if I decide for error simple doesn't work and Ignore nothing happen... some more information about this self referencia loop?
var u = usuario.SingleOrDefault(x => x.TipoUsuario == "A" || x.TipoUsuario == "W");
JsonSerializerSettings setting = new JsonSerializerSettings();
setting.ReferenceLoopHandling = ReferenceLoopHandling.Error; //.Serialize .Ignore
Page.ClientScript.RegisterClientScriptBlock(this.GetType(),"usuario", "var usuario=" + JsonConvert.SerializeObject(u, Formatting.None, setting) + ";");
Update ------
I code the following
string jsU = JsonConvert.SerializeObject(u,Formatting.None,new JsonSerializerSettings { PreserveReferencesHandling = PreserveReferencesHandling.Objects, ReferenceLoopHandling = ReferenceLoopHandling.Ignore });
and is workign but the only thing wrongs is that in the json object comes all the information about the columns of subsonic 3 and a BIG chunk of text explain it... does any one know how to not SEND this part of the object??
Without knowing more about you object model it is hard to provide a definitive answer, but I would take a look at the ReferenceLoopHandling enum.
You're calling string SerializeObject(object value) on JsonConvert. Try the string SerializeObject(object value, Formatting formatting, JsonSerializerSettings settings) method instead. The JsonSerializerSettings settings parameter lets you set a bunch of things, including the ReferenceLoopHandling ReferenceLoopHandling { get; set; } property.
You can try these values:
public enum ReferenceLoopHandling
{
Error,
Ignore,
Serialize
}
Obviously, Error is the default and that's what you're getting. Perhaps one of the others will help.
My main question here is dealing with the pramas map when having a one-to-many relationship managed within one dynamic form, as well as best practices for dealing with one-to-many when editing/updating a domain object through the dynamic form. The inputs for my questions are as follows.
I have managed to hack away a form that allows me to create the domain objects shown below in one Dynamic form, since there is no point in having a separate form for creating phone numbers and then assigning them to a contact, it makes sense to just create everything in one form in my application. I managed to implement something similar to what I have asked in my Previous Question (thanks for the people who helped out)
class Contact{
String firstName
String lastName
// ....
// some other properties
// ...
static hasMany = [phones:Phone]
static mapping = {
phones sort:"index", cascade: "all-delete-orphan"
}
}
class Phone{
int index
String number
String type
Contact contact
static belongsTo = [contact:Contact]
}
I basically managed to get the values from the 'params' map and parse them on my own and create the domain object and association manually. I.e. i did not use the same logic that is used in the default scaffolding, i.e.
Contact c = new Contact(params)
etc...., i just looped through all the params and hand crafted my domain objects and saved them and everything works out fine.
My controller has code blocks that look like this (this is stripped down, just to show a point)
//create the contact by handpicking params values
def cntct = new Contact()
cntct.firstName = params.firstName
cntct.lastName = params.lastName
//etc...
//get array of values for number,type
def numbers = params['phone.number']
def types = params['phone.type']
//loop through one of the arrays and create the phones
numbers.eachWithIndex(){ num, i ->
//create the phone domain object from
def phone = new Phone()
phone.number = num
phone.type = types[i]
phone.index = i
cntct.addToPhones(phone)
}
//save
My questions are as follows:
What is the best practice of handeling such a situation, would using Command objects work in this case, if yes where can i found more info about this, all the examples I have found during my search deal with one-to-one relationships, I couldn't find an example for one-to-many?
What is the best way to deal with the relatiohsips of the phones in this case, in terms of add/removing phones when editing the contact object. I mean the creation logic is simple since I have to always create new phones on save, but when dealing with updating a contact, the user might have removed a phone and/or editing an exiting one and/or added some new phones. Right now what I do is just delete all the phones a contact has and re-create them according to what was posted by the form, but I feel that's not the best way to do it, I also don't think looping over the existing ones and comparing with the posted values and doing a manual diff is the best way to do it either, is there a best practice on how to deal with this?
Thanks, hopefully the questions are clear.
[edit] Just for more information, phone information can be added and deleted dynamically using javascript (jquery) within the form [/edit]
disclaimer: i do not know if the following approach works when using grails. Let me know later.
See better way for dynamic forms. The author says:
To add LineItems I have some js that calculates the new index and adds that to the DOM. When deleting a LineItem i have to renumber all the indexes and it is what i would like to avoid
So what i do
I have a variable which stores the next index
var nextIndex = 0;
When the page is loaded, i perform a JavaScript function which calculates how many child The collection has and configure nextIndex variable. You can use JQuery or YUI, feel free.
Adding a child statically
I create a variable which store the template (Notice {index})
var child = "<div>"
+= "<div>"
+= "<label>Name</label>"
+= "<input type="text" name=\"childList[{index}].name\"/>"
+= "</div>"
+= "</div>"
When the user click on the Add child button, i replace {index} - by using regex - by the value stored in the nextIndex variable and increment by one. Then i add to the DOM
See also Add and Remove HTML elements dynamically with Javascript
Adding a child dinamically
Here you can see The Paolo Bergantino solution
By removing
But i think it is the issue grow up when deleting. No matter how many child you remove, does not touch on the nextIndex variable. See here
/**
* var nextIndex = 3;
*/
<input type="text" name="childList[0].name"/>
<input type="text" name="childList[1].name"/> // It will be removed
<input type="text" name="childList[2].name"/>
Suppose i remove childList1 What i do ??? Should i renumber all the indexes ???
On the server side i use AutoPopulatingList. Because childList1 has been removed, AutoPopulatingList handles it as null. So on the initialization i do
List<Child> childList = new AutoPopulatingList(new ElementFactory() {
public Object createElement(int index) throws ElementInstantiationException {
/**
* remove any null value added
*/
childList.removeAll(Collections.singletonList(null));
return new Child();
}
});
This way, my collection just contains two child (without any null value) and i do not need to renumber all the indexes on the client side
About adding/removing you can see this link where i show a scenario wich can gives you some insight.
See also Grails UI plugin
Thanks,
Your answer brought some insight for me to do a wider search and I actually found a great post that covers all the inputs in my question. This is just a reference for anyone reading this. I will write a blog entry on how I implemented my case soon, but this link should provide a good source of ino with a working exmaple.
http://www.2paths.com/2009/10/01/one-to-many-relationships-in-grails-forms/
Most of the time I use ajax to manage such problem.
So when the user clicks add new phone I get the template UI from the server for manageability purpose ( the UI just same GSP template that I use to edit, update the phone), so this way you are not mixing your UI with your js code, whenever you want to change the UI you have to deal only with our GSP code.
Then after getting the UI I add it to the page using jquery DOM manipulation. Then after filling the form when they hit add(save) the request is sent to the server via ajax and is persisted immediately.
When the user clicks edit phone the same UI template is loaded from the server filled with existing phone data, then clicking update will update the corresponding phone immediately via ajax, and same thing applies to delete operation.
But one day I got an additional scenario for the use case that says, "until I say save contact no phone shall be saved on the backend, also after adding phones to the contact on the ui if navigate away to another page and come back later to the contact page the phones I added before must be still there." ugh..
To do this I started using the Session, so the above operations I explained will act on the phone list object I stored on the session instead of the DB. This is simple perform all the operation on the phonesInSession but finally dont forget to do this(delete update):
phonesToBeDeleted = phonesInDB - phonesInSession
phonesToBeDeleted.each{
contact.removeFromPhones(it)
it.delete()
}
I know I dont have to put a lot of data in session but this is the only solution I got for my scenario.
If someone has got similar problem/solution please leave a comment.
First, in all your input fields names you add an #:
<input type="text" name="references[#].name"/>
Second, add call a function before submitting:
<g:form action="save" onsubmit="replaceAllWildCardsWithConsecutiveNumbers();">
Third, this is the code for the function that you call before submitting the form:
function replaceAllWildCardsWithConsecutiveNumbers(){
var inputs = $('form').find("[name*='#']");
var names = $.map(inputs, function(el) { return el.name });
var uniqueNames = unique(names);
for (index in uniqueNames) {
var uniqueName = uniqueNames[index];
replaceWildCardsWithConsecutiveNumbers("input", uniqueName);
replaceWildCardsWithConsecutiveNumbers("select", uniqueName);
}
}
function unique(array){
return array.filter(function(el, index, arr) {
return index === arr.indexOf(el);
});
}
function replaceWildCardsWithConsecutiveNumbers(inputName, name){
counter = 0;
$(inputName + "[name='" + name + "']").each(function (i, el) {
var curName = $(this).attr('name');
var newName = curName.replace("#", counter);
$(this).attr('name', newName);
counter += 1;
});
}
Basically, what the code for replaceAllWildCardsWithConsecutiveNumbers() does, is to create a list for all input (or select) elements whose name contains an #. Removes the duplicates. And then iterates over them replacing the # with a number.
This works great if you have a table and you are submitting the values to a command object's list when creating a domain class for the first time. If you are updating I guess you'll have to change the value of counter to something higher.
I hope this helps someone else since I was stuck on this issue for a while myself.