Insert only if not exists, if exists do nothing

[rksprst]

Hi,

I want to insert a value only if it doesn't already exists. If it
already exists, I don't want to do anything.

I want to avoid checking if the value is there as this insert will
happen many many times a second. "upsert" isn't what I want as I don't
want to update if it exists. Is there something else that can
accomplish this task?

Thanks,
Alex

[Eliot Horowitz]

If you create a unique index on whatever your unique constraint is,
then that's what will happen.

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[rksprst]

So after I create the unique insert, do I just do a normal insert?

[Eliot Horowitz]

yes

[rksprst]

It seems that I can only insert a whole document. I just want to
update a value in the document. Is there a way to do it with the
Update.Set or similar syntax? I also need to use a query so that it
will find do the set only on the documents that fit a specified
query.

e.g. I want to do the following:

QueryComplete query = Query.And(
Query.EQ("MemGuid", memGuid),
Query.EQ("Sessions.SessionId", sessionId)
);
var update = Update.PushAll("Sessions.$.Events",
events.ToArray()).Set("Last ", utcNow);

database.GetCollection<TrackedUser>("TrackedItems").Update(query,
update, UpdateFlags.Upsert, SafeMode.True);

But where the .Set("Last ", utcNow) only sets the value if it is null
(i.e. the value doesn't exist).

I'm using the 10gen c# driver. Also, per my other question on here
( http://groups.google.com/group/mongodb-user/browse_thread/thread/1746866abb30abca#
) I want to batch the requests.

[Robert Stam]

You'll probably have to break it up into two operations so you can
test that Last is not null in one of them. I'm not aware of any
conditional $set update modifiers.

Also, a good way to experiment (and to ask the questions) is to use
the Mongo shell. Once you get it working there you can figure out how
to express the same update in C#. If you use temporary variables for
your query and update arguments (as you did) you can use the ToJson()
method to see if they are equivalent to the query and update that
worked in the shell.

On Jan 18, 7:23 pm, rksprst <alex.kamin...@gmail.com> wrote:
> It seems that I can only insert a whole document. I just want to
> update a value in the document. Is there a way to do it with the
> Update.Set or similar syntax? I also need to use a query so that it
> will find do the set only on the documents that fit a specified
> query.
>
> e.g. I want to do the following:
>
>             QueryComplete query = Query.And(
>                     Query.EQ("MemGuid", memGuid),
>                     Query.EQ("Sessions.SessionId", sessionId)
>                 );
>             var update = Update.PushAll("Sessions.$.Events",
> events.ToArray()).Set("Last ", utcNow);
>
> database.GetCollection<TrackedUser>("TrackedItems").Update(query,
> update, UpdateFlags.Upsert, SafeMode.True);
>
> But where the .Set("Last ", utcNow) only sets the value if it is null
> (i.e. the value doesn't exist).
>
> I'm using the 10gen c# driver. Also, per my other question on here

> (http://groups.google.com/group/mongodb-user/browse_thread/thread/1746...

[rksprst]

I'm going to try doing it with Query.EQ("Last", null). Would that
work?

Also, I have around 10 fields where I want to update them if they are
not null. It seems like I would have to do 10 queries to figure out
which one is null or not. Is that correct?

[Robert Stam]

You have to use Query.EQ("Last", BsonNull.Value).

If someone figures out how to do what you want to do in the shell we
can translate that to C#, otherwise I think it is one update for every
field that you want to check for null.

[kishore kumar]

How do we do it in a shard environment.