Querying Mongodb documents for array properties

Date published30.04.2017Time to read2 minutes read

Ladies and gents, I’m just posting one short reminder to myself and anyone keen to find out how do we query array type fields in Mongodb.

Let’s start by inserting couple of documents (using Mongodb shell) which we’ll use for querying afterwards:

db.developers.insertMany([
  { name: "John", languages: ["java", "php", "javascript"] },
  { name: "Jack", languages: ["java", "c", "c++"] },
  { name: "Jim", languages: ["node", "java"] }
]);

Now, when we run the following command in shell:

db.developers.find();

Command output confirms all test documents are successfully stored:

{
    "_id" : ObjectId("587e6ec738cbd11c2dc46932"),
    "name" : "John",
    "languages" : [
        "java",
        "php",
        "javascript"
    ]
}
{
    "_id" : ObjectId("587e6ec738cbd11c2dc46933"),
    "name" : "Jack",
    "languages" : [
        "java",
        "c",
        "c++"
    ]
}
{
    "_id" : ObjectId("587e6ec738cbd11c2dc46934"),
    "name" : "Jim",
    "languages" : [
        "node",
        "java"
    ]
}

Now, say you want to find all documents that have “java” as the first entry in languages array field, we do by using following syntax:

db.developers.find({ "languages.0": "java" });

Command output confirms we matched correct document(s):

{
    "_id" : ObjectId("587e6ec738cbd11c2dc46932"),
    "name" : "John",
    "languages" : [
        "java",
        "php",
        "javascript"
    ]
}
{
    "_id" : ObjectId("587e6ec738cbd11c2dc46933"),
    "name" : "Jack",
    "languages" : [
        "java",
        "c",
        "c++"
    ]
}

Array position is indexed as expected starting by zero, so in case we want all docs having “java” at second position, we do it like this:

db.developers.find({ "languages.1": "java" });

Next, if we want to list all documents that contain “java” at any position inside languages array field, we do it like this:

db.developers.find({ languages: "java" });

Command output lists all initially inserted documents:

{
    "_id" : ObjectId("587e6ec738cbd11c2dc46932"),
    "name" : "John",
    "languages" : [
        "java",
        "php",
        "javascript"
    ]
}
{
    "_id" : ObjectId("587e6ec738cbd11c2dc46933"),
    "name" : "Jack",
    "languages" : [
        "java",
        "c",
        "c++"
    ]
}
{
    "_id" : ObjectId("587e6ec738cbd11c2dc46934"),
    "name" : "Jim",
    "languages" : [
        "node",
        "java"
    ]
}

Finally, if we want to find all documents that have languages field exact to let’s say:

["java", "php", "javascript"]

we do it like this:

db.developers.find({ languages: ["java", "php", "javascript"] });

Command output prints something like:

{
  "_id": ObjectId("587e6ec738cbd11c2dc46932"),
  "name": "John",
  "languages": ["java", "php", "javascript"]
}

I’m primary keeping this as a quick reminder to myself, but will be very happy if someone else finds it useful!

That was all for today! Hope you liked it!