mongodb: insert if not exists

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 failsE11000 duplicate key error index: foo.test.$a_1  dup key: { : 1.0 }