Append a string to the end of an existing field in MongoDB

Question

I have a document with a field containing a very long string. I need to concatenate another string to the end of the string already contained in the field.

The way I

Answer 1

Old topic but i had the same problem. Since mongo 2.4, you can use $concat from aggregation framework.

Example

Consider these documents :

{
    "_id" : ObjectId("5941003d5e785b5c0b2ac78d"),
    "title" : "cov"
}

{
    "_id" : ObjectId("594109b45e785b5c0b2ac97d"),
    "title" : "fefe"
}

Append fefe to title field :

db.getCollection('test_append_string').aggregate(
    [
        { $project: { title: { $concat: [ "$title", "fefe"] } } }
    ]
)

The result of aggregation will be :

{
    "_id" : ObjectId("5941003d5e785b5c0b2ac78d"),
    "title" : "covfefe"
}

{
    "_id" : ObjectId("594109b45e785b5c0b2ac97d"),
    "title" : "fefefefe"
}

You can then save the results with a bulk, see this answer for that.