Mongodb Create Collection

MongoDB Create Collection

In this section, we will introduce how to use MongoDB to create a collection.

MongoDB uses the createCollection() method to create a collection.

Syntax:

db.createCollection(name, options)

Parameter Description:

name: The name of the collection to be created.
options: Optional parameters, specifying options related to memory size and indexes.

The options can be the following parameters:

Parameter Name	Type	Description	Example Value
`capped`	Boolean	Whether to create a fixed-size collection.	`true`
`size`	Number	Maximum size of the collection (in bytes). Only effective when `capped` is true.	`10485760` (10MB)
`max`	Number	Maximum number of documents allowed in the collection. Only effective when `capped` is true.	`5000`
`validator`	Object	An expression for document validation.	`{ $jsonSchema: { ... }}`
`validationLevel`	String	Specifies the strictness of document validation. `"off"`: No validation. `"strict"`: Insert and update operations must pass validation (default). `"moderate"`: Only existing documents must pass validation upon update; new documents do not need to.	`"strict"`
`validationAction`	String	Specifies the action to take when document validation fails. `"error"`: Prevents insertion or update (default). `"warn"`: Allows insertion or update but issues a warning.	`"error"`
`storageEngine`	Object	Specifies the storage engine configuration for the collection.	`{ wiredTiger: { ... }}`
`collation`	Object	Specifies the default collation for the collection.	`{ locale: "en", strength: 2 }`

When inserting documents, MongoDB first checks the size field of a capped collection, then checks the max field.

An example of creating a collection with these options:

Example

db.createCollection("myComplexCollection",{
    capped:true,
    size:10485760,
    max:5000,
    validator:{ $jsonSchema:{
        bsonType:"object",
        required:["name","email"],
        properties:{
            name:{
                bsonType:"string",
                description:"Must be a string and is required"
            },
            email:{
                bsonType:"string",
                pattern:"^.+@.+$",
                description:"Must be a valid email address"
            }
        }
    }},
    validationLevel:"strict",
    validationAction:"error",
    storageEngine:{
        wiredTiger:{ configString:"block_compressor=zstd"}
    },
    collation:{ locale:"en", strength:2}
});

This example creates a collection with the following characteristics:

Fixed size, maximum 10MB, storing up to 5000 documents.
Documents must contain name and email fields, where name must be a string and email must be in a valid email format.
Validation level is strict; failed validation will prevent insertion or update.
Uses the WiredTiger storage engine, specifying the block compressor as zstd.
Default uses English collation rules.

Example

Create a tutorial collection in the test database:

> use test
switched to db test
> db.createCollection("tutorial")
{ "ok" : 1 }
>

To view existing collections, you can use the show collections or show tables command:

> show collections
tutorial
system.indexes
>

Below is the usage of createCollection() with a few key parameters:

Creates a capped collection with a maximum size of 5MB (5242880 bytes) and a maximum of 5000 documents.

db.createCollection("myCappedCollection", { capped: true, size: 5242880, max: 5000 });

In MongoDB, you don't need to create a collection explicitly. When you insert some documents, MongoDB will automatically create the collection.

> db.mycol2.insert({"name" : ""})
> show collections
mycol2
...

Creates a capped collection with a maximum size of 1MB (1048576 bytes):

db.createCollection("myCappedCollection", { capped: true, size: 1048576 });

The following example creates a validator for the myCollection collection, requiring documents to have name and age fields, where name must be a string and age must be a non-negative integer.

Example

db.createCollection("myCollection",{
    validator:{ $jsonSchema:{
        bsonType:"object",
        required:["name","age"],
        properties:{
            name:{
                bsonType:"string",
                description:"Must be a string and is required"
            },
            age:{
                bsonType:"int",
                minimum:0,
                description:"Must be an integer and is required"
            }
        }
    }}
});

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