mongodb: insert if not exists

Question

Sounds like you want to do an "upsert". MongoDB has built-in support for this. Pass an extra parameter to your update() call: {upsert:true}. For example:

key = {'key':'value'}
data = {'key2':'value2', 'key3':'value3'};
coll.update(key, data, upsert=True); #In python upsert must be passed as a keyword argument

This replaces your if-find-else-update block entirely. It will insert if the key doesn't exist and will update if it does.

Before:

{"key":"value", "key2":"Ohai."}

After:

{"key":"value", "key2":"value2", "key3":"value3"}

You can also specify what data you want to write:

data = {"$set":{"key2":"value2"}}

Now your selected document will update the value of "key2" only and leave everything else untouched.

As of MongoDB 2.4, you can use $setOnInsert (http://docs.mongodb.org/manual/reference/operator/setOnInsert/)

Set 'insertion_date' using $setOnInsert and 'last_update_date' using $set in your upsert command.

To turn your pseudocode into a working example:

now = datetime.utcnow()
for document in update:
    collection.update_one(
        filter={
            '_id': document['_id'],
        },
        update={
            '$setOnInsert': {
                'insertion_date': now,
            },
            '$set': {
                'last_update_date': now,
            },
        },
        upsert=True,
    )

You could always make a unique index, which causes MongoDB to reject a conflicting save. Consider the following done using the mongodb shell:

> db.getCollection("test").insert ({a:1, b:2, c:3})
> db.getCollection("test").find()
{ "_id" : ObjectId("50c8e35adde18a44f284e7ac"), "a" : 1, "b" : 2, "c" : 3 }
> db.getCollection("test").ensureIndex ({"a" : 1}, {unique: true})
> db.getCollection("test").insert({a:2, b:12, c:13})      # This works
> db.getCollection("test").insert({a:1, b:12, c:13})      # This fails
E11000 duplicate key error index: foo.test.$a_1  dup key: { : 1.0 }

You may use Upsert with $setOnInsert operator.

db.Table.update({noExist: true}, {"$setOnInsert": {xxxYourDocumentxxx}}, {upsert: true})