db.pets.find();

db.pets.find({
    $or: [
        {
            type: "dog"
        }
    ]
});

db.pets.find({
    $or: [
        {
            type: "dog"
        }
    ]
}).count(); //

db.pets.find({
    $or: [
        {
            type: "dog"
        },
        {
            type: "bird"
        }
    ]
});

db.pets.find({
    age: {$gte: 4},
    $or: [
        {
            type: "dog"
        },
        {
            type: "bird"
        },
    ]
});