JIYIK CN >

In this article, we will address how to use the MongoDB distinct() method to return unique values. In addition, returning unique values ​​in arrays and fields is discussed.

In MongoDB, sometimes you may want to present or return unique values, you can do this using the distinct() method.

distinct()The method generates an array of distinct values ​​for a given field across all collections or views in a single collection or view and helps you return unique values ​​for a specified field in the mongo shell.

distinct() function in MongoDB

grammar:

db.collection.distinct(field, query, options)

In MongoDB, the function must have two required parameters called field and query operator. The field parameter is the field in which you want the distinct() method to get unique values.

The query parameter specifies the document from which the distinct values ​​should be fetched. You can send collateral options parameters to the function.

请注意If the value of the specified field is an array, distinct distinct()() will treat each array element as a separate value. For example, if the value of the field is [10, [10], 10], distinct() will treat 10, [10], and 10 as separate values.

Use the distinct() function to return unique values

Let's use distinct()the function to return unique values ​​in MongoDB. The following collection will be used for the first example.

db.movies.find().pretty()
{
        "_id" : ObjectId("60322d3501cd70079c48cb65"),
        "title" : "Enchanted",
        "year" : 2006,
        "score" : 10,
        "rating" : "PG",
        "__v" : 0
}
{
        "_id" : ObjectId("60322d3501cd70079c48cb67"),
        "title" : "Final Destination II",
        "year" : 2015,
        "score" : 10,
        "rating" : "PG-13",
        "__v" : 0
}
{
        "_id" : ObjectId("6190189ef5c8903629012fe1"),
        "title" : "Fifty Shades of Grey",
        "year" : 2015,
        "score" : 10,
        "rating" : "NC-17",
        "__v" : 0
}

Returns unique or distinct values ​​for a field in MongoDB

The movies collection above returns unique values ​​for the field specified in this example. Suppose you want unique values ​​in the ratings field.

Query:

db.movies.distinct( "rating" )
[ null, "", "NC-17", "PG", "PG-13"]

After using the above query, distinct()the function has successfully helped you return unique values ​​for a collection in MongoDB.

Return unique values ​​for embedded fields in MongoDB

In this example, returning unique values ​​for an embedded field is shown. However, the collection used in the previous example does not contain an embedded field.

Therefore, a new collection will be used as shown below.

db.drones.find().pretty()
{
        "_id" : ObjectId("61673f46b34f185eb7b2bf0c"),
        "utility" : [
                "Natural Resource Exploration",
                "Remote sensing",
                "Real estate and construction",
                "Recreation",
                "Delivery"
        ],
        "onSale" : false,
        "name" : "Nimbari Gryphon Medeta 65",
        "price" : 77500,
        "weight" : "77 kilograms",
        "additionalDetails" : {
                "material" : "carbon fiber",
                "moreUses" : [
                        "Precision Agriculture",
                        "Land Inspection",
                        "Water Inspection",
                        "Cinematography"
                ]
        }
}
{
        "_id" : ObjectId("61673f46b34f185eb7b2bf0d"),
        "utility" : [
                "Natural Resource Exploration",
                "Remote sensing",
                "Real estate and construction",
                "Recreation",
                "Delivery"
        ],
        "onSale" : false,
        "name" : "X-Strimmer Eye",
        "price" : 23500,
        "weight" : "24 kilograms",
        "additionalDetails" : {
                "material" : "glass fiber",
                "moreUses" : [
                        "Precision Agriculture",
                        "Cinematography"
                ]
        }
}
{
        "_id" : ObjectId("61673f46b34f185eb7b2bf0e"),
        "utility" : [
                "Natural Resource Exploration",
                "Remote sensing",
                "Real estate and construction",
                "Recreation",
                "Delivery"
        ],
        "onSale" : false,
        "name" : "Khai Balemosh Shefqa TRX",
        "price" : 120500,
        "weight" : "80 kilograms",
        "additionalDetails" : {
                "material" : "aluminum",
                "moreUses" : [
                        "Precision Agriculture",
                        "Land Inspection"
                ]
        }
}

The following query returns unique values ​​from all embedded fields in the above database collection.

Query:

db.drones.distinct( "additionalDetails.material" )
[ "aluminum", "carbon fiber", "glass fiber"]

Returns the unique values ​​of an embedded array field

Using the distinct() function, you can use the same collection above to return unique values ​​from an embedded array field using the distinct() function.

Query:

db.drones.distinct( "additionalDetails.moreUses" )
["Cinematography","Land Inspection"]

In this MongoDB tutorial article, you will learn in detail about different functions with collections. Returning arrays and unique values ​​in a field or embedded fields are also explained with code snippets.