Here is an example:
r.db('my_db').table('my_table').get('my_record_id_123')
The above code works fine, but returns the record. The records in this table are huge. Is there a way to check if the record with that specific id exists or not without returning the record itself?
Perhaps this is what you want (it will return true if the record exists or false otherwise):
r.db('my_db')
.table('my_table')
.getAll('my_record_id_123')
.count()
.eq(1)
returns number
r.db('my_db')
.table('my_table')
.count(function(user){
return user('id').eq(1121)
})
r.db('my_db')
.table('my_table')
.getAll('my_record_id_123')
.contains()
This works for me :)
Related
After looking at some SO questions and issues on RethinkDB github, I failed to come to a clear conclusion if atomic Upsert is possible?
Essentially I would like to perform the same operation as ZINCRBY using Redis.
If member does not exist in the sorted set, it is added with increment
as its score (as if its previous score was 0.0). If key does not
exist, a new sorted set with the specified member as its sole member
is created.
The current implementation appears to differ from almost all databases that I have used. With the data being replaced or inserted not updated. This is a simple use case, like update the last visit, update the number of clicks, update a product quantity. So I must be missing something very obvious, because I cannot see a simple way to do this.
Yes, it is possible. After get on the key, perform an atomic replace. Something like this might work:
function set_or_increment_score(player, points){
return r.table('scores').get(player).replace(
row =>
{ id: player,
score: r.branch(
row.eq(null),
points,
row('score').add(points))
});
}
It has the following behaviour:
> set_or_increment_score("alice", 1).run(conn)
{ inserted: 1 }
> set_or_increment_score("alice", 2).run(conn)
{ replaced: 1 }
It works because get returns null when the document doesn't exist, and a replace on a non-existing document tuns into an insert. See the documentation for replace
So I end up using the following code to go around the no Update issue.
r.db("test").table("t").insert(
{id:"A", type:"player", species:"warrior", score:0, xp:0, armor:0},
{conflict: function(id, oldDoc, newDoc) {
return newDoc.merge(oldDoc).merge(
{armor: oldDoc("armor").add(1)});
}
}
)
Do you think this is more readable/elegant or do you see any issues with the code compared to your sample?
I found an answer for finding all documents in a table with missing fields in this SO thread RethinkDB - Find documents with missing field, however I want to filter according to a missing field AND a certain value in a different field.
I want to return all documents that are missing field email and whose isCurrent: value is 1. So, I want to return all current clients who are missing the email field, so that I can add the field.
The documentation on rethink's site does not cover this case.
Here's my best attempt:
r.db('client').table('basic_info').filter(function (row) {
return row.hasFields({email: true }).not(),
/*no idea how to add another criteria here (such as .filter({isCurrent:1})*/
}).filter
Actually, you can do it in one filter. And, also, it will be faster than your current solution:
r.db('client').table('basic_info').filter(function (row) {
return row.hasFields({email: true }).not()
.and(row.hasFields({isCurrent: true }))
.and(row("isCurrent").eq(1));
})
or:
r.db('client').table('basic_info').filter(function (row) {
return row.hasFields({email: true }).not()
.and(row("isCurrent").default(0).eq(1));
})
I just realized I can chain multiple .filter commands.
Here's what worked for me:
r.db('client').table('basic_info').filter(function (row) {
return row.hasFields({email: true }).not()
}).filter({isCurrent: 1}).;
My next quest: put all of these into an array and then feed the email addresses in batch
i have the following code snippet.
in which i just want to return PartyName as a string.
but i get the error:"Cannot implicity convert type 'System.Linq.Iqueryable to string"
if i want to return only string then what to do?
please help me.
return objDatabase.FAPARs
.Where(f => (f.PARTY_CODE == "P003"))
.Select(f => f.PARTY_NAME);
An IQueryable<string> represents a query which could return any number of strings. You want one string - so you need to decide what to do in various situations:
What do you want to happen if the query has no results?
What do you want to happen if the query has one result? (I assume this is simple :)
What do you want to happen if the query has more than one result?
The set of methods which allow you to determine all of this are:
Single - fail if there isn't exactly one result
SingleOrDefault - fail if there's more than one result, return null if there are no results
First - fail if there are no results, return the first of many
FirstOrDefault - return null if there are no results, or the first of many
Last - fail if there are no results, return the last of many
LastOrDefault - return null if there are no results, or the last of many
In each case, "fail" means "throw an exception". (IIRC it's always InvalidOperationException, at least in LINQ to Objects, but I could be wrong.)
So if you're querying by an ID which must exist (i.e. it's a bug if it doesn't) then Single is probably appropriate. If you're querying by an ID which may not exist, then use SingleOrDefault and check whether the return value is null. If you're not querying by an ID, you probably want to use FirstOrDefault or just iterate over the results.
(Note that the default value being null is due to this being a query returning strings, and string being a reference type. In general it's the default value of the element type - so if you had an IQueryable<int>, the default returned would be 0.)
Try
return objDatabase.FAPARs .Where(f => (f.PARTY_CODE == "P003")) .Select(f => f.PARTY_NAME).SingleOrDefault();
Try this:
return objDatabase.FAPARs.Where(f => (f.PARTY_CODE == "P003")).Single(f => f.PARTY_NAME);
return objDatabase.FAPARs.FirstOrDefault(f => f.PARTY_CODE.Equals("P003")).PARTY_NAME
return objDatabase.FAPARs.OfType<FAPAR>()
.Where(f => (f.PARTY_CODE == PartyCode && f.COMP_NO == ComCode))
.Select(f => f.PARTY_NAME).SingleOrDefault();
Seems like such a simple thing, but I can't get my query to return the number of records in a group. Here's my statement:
public function getGroupCount($user_id)
{
$q = Doctrine_Query::create()
->select('ss.*')
->from('SalarySurvey ss')
->where('ss.user_id=?', $user_id)
->groupBy('created_at')
->execute();
return $q->rowCount();
}
rowCount() does not work in the above query.
It might also be helpful to know that this is being used in a foreach statement.
As CappY suggested, this is not possible in Doctrine 1.2, as far as I know. As a work-around, I was able to finally get a count for each grouping by adding another field to the table and setting that field the same for each group at save time. Then I changed my query to pull that field and just did a simple:
$q->count();
Never work with Doctrine 1.2, but can't U use php's count function or SELECT COUNT() AS 'cnt' ?
return count($q);
I have an exchange rate table. I need to get current rate and previous rate and then compare results.
I can get first record using FirstOrDefault.
When I am using ElementAtOrDefault, this error shows "The query operator 'ElementAtOrDefault' is not supported". How can I get the second record?
You can try this:
var query=data.Skip(1).Take(1);
Take() returns null if the element is not there (so is equivalent to FirstOrDefault()).
If you'd rather an exception was thrown (cos the second element is not there) like First() then use:
Skip(1).Single()
Try this simple implementation this might be useful
var query= (from p in db.Person where p.Person == person_id select p);
var firstResult = query.First();
var secondResult = query.Skip(1).Take(1).Single();
var thirdResult = query.Skip(2).Take(1).Single();
There's a detail not explicitly mentioned here: FirstOrDefault returns an Element, Skip(1).Take(1) returns a set of 1 element; i.e. the type returned by Skip(1).Take(1) is IEnumerable, while FirstOrDefault is not.
If you use
.Take(2)
you will get the first and second.
EDIT- If you need both the first and second, then the above will be more efficient than runing your query twice:
.Take(1)
.Skip(1).Take(1)
Collection.ElementAt(1)
will fetch the second record in the collection.
Select top 2, then select second element.
As John Anderson already pointed out Skip(1).Take(1) returns an IEnumerable of size 1.
In order to get the 2nd entry itself or else a null (i.e. no exceptions), I'm using the following:
var secondEntry = collection?.Skip(1)?.FirstOrDefault();
It may not work in your specific case, but may be useful for use cases of other.
Use .Skip(1) method