Let’s assume we have a collection with lot of data in a single document. We have a countries
collection. We are going to select just few fields we want,
// Query without selection
db.posts.find({});
// Result will look like
[
{
_id: ObjectId('5e14ba178e47a9a3b8b7af52'),
name: 'Estonia',
shortName: 'EST',
cities: ['Tartu', 'Tallinn', 'Viljandi'],
},
{
_id: ObjectId('5e14ba3c8e47a9a3b8b7af5a'),
name: 'India',
shortName: 'IND',
cities: ['Chennai', 'Mumbai', 'Delhi'],
},
{
_id: ObjectId('5e14ba558e47a9a3b8b7af62'),
name: 'United states of America',
shortName: 'USA',
cities: [],
},
{
_id: ObjectId('5e14ba6a8e47a9a3b8b7af67'),
name: 'Sweden',
shortName: 'SE',
},
];
Now, I want to select only the name
field and display only the result with name
field.
Inorder to do that, we need to first understand the mongoDB query syntax
db.countries.find(
// For basic filtering based on the key values passed
{},
// for selecting the fields
{}
);
You can pass the second parameter to the find
method. It will work for findOne
too.
Now let’s select the name
field.Here you need to learn one more trick, The key will be the field you want to select, what about the value?Value will be 1
for selecting a field. 0
for deselecting a field.
Let’s see it as example
Selecting only country name field
// Query with name selection
db.posts.find({}, { name: 1 });
// Result will look like
[
{
_id: ObjectId('5e14ba178e47a9a3b8b7af52'),
name: 'Estonia',
},
{
_id: ObjectId('5e14ba3c8e47a9a3b8b7af5a'),
name: 'India',
},
{
_id: ObjectId('5e14ba558e47a9a3b8b7af62'),
name: 'United states of America',
},
{
_id: ObjectId('5e14ba6a8e47a9a3b8b7af67'),
name: 'Sweden',
},
];
Here we have successfully selected only the name
field. Wait? there is also the _id
field without we pass it explicitly?
by default, mongo query will always include the _id
field.
Deselecting any field
Let’s deselect the _id
field itself, it’s the same way,
// Query with name selection and _id deselection
db.posts.find({}, { name: 1, _id: 0 });
// Result will look like
[
{
name: 'Estonia',
},
{
name: 'India',
},
{
name: 'United states of America',
},
{
name: 'Sweden',
},
];
Hope you find this tutorial series helpful. Next we will learn more into this series. Share it with your groups and happy learning 🤗
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