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Reading/Writing Database
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Last updated: 2024-01-15 14:34:08
Reading/Writing Database
Last updated: 2024-01-15 14:34:08
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After you connect to the database instance, you can create databases and write data to them.

Creating a Database

The syntax to create a MongoDB database is as follows: 
use DATABASE_NAME
Create a database named "myFirstDB" and insert a document to it:
> use myFirstDB
switched to db myFirstDB
> db.myFirstDB.insert({"test":"myFirstDB"})
WriteResult({ "nInserted" : 1 })
Show the database you created:
> show dbs
admin      0.000GB
config     0.000GB
local      0.041GB
myFirstDB  0.000GB

Creating a Collection

In MongoDB, you can use the createCollection() method to create a collection. Syntax:
db.createCollection(name, options)
Parameter description:
name: the name of the collection to create
options: (optional) options of memory size and index
options Field
Type
Description
capped
BOOL
Whether to set a maximum size in bytes for the collection. Valid values: true (the size field must be specified), false (default)
autoIndexId
BOOL
Whether to automatically create an index on the \\_id field. Valid values: true, false (default)
size
number
The maximum size in bytes of the collection
max
number
The maximum number of documents in the collection
Create a collection named "FirstCol" in the myFirstDB database:
> use myFirstDB
switched to db myFirstDB
> db.createCollection("FirstCol")
{
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1634821900, 2),
                "signature" : {
                        "hash" : BinData(0,"WFu7yj8wjeUBWG3b+oT84Q8wIw8="),
                        "keyId" : NumberLong("6990600483068968961")
                }
        },
        "operationTime" : Timestamp(1634821900, 2)
}
Show the collection you created:
> show collections
FirstCol
The following sample shows that the FirstCol collection you created can have up to 10,000 documents whose total size cannot exceed 6,142,800 bytes.
> db.createCollection("FirstCol", { capped : true, autoIndexId : true, size : 6142800, max : 10000 } )
{
        "note" : "the autoIndexId option is deprecated and will be removed in a future release",
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1634821879, 1),
                "signature" : {
                        "hash" : BinData(0,"EuIbp2fu9Yh38HOBHLgYqljdKaE="),
                        "keyId" : NumberLong("6990600483068968961")
                }
        },
        "operationTime" : Timestamp(1634821879, 1)
}

Inserting a Document

In MongoDB, you can use the insert() or save() method to insert a document to a collection, as shown below:
> db.FirstCol.insert({name:"Jane Smith",sex:"Female",age:25,status:"A"})
WriteResult({ "nInserted" : 1 })
Show the document inserted to the collection:
> db.FirstCol.find()
{ "_id" : ObjectId("61716957a6fe1ef4d7eae979"), "name" : "Jane Smith", "sex" : "Female", "age" : 25, "status" : "A" }
You can use db.collection.insertMany() to insert one or more documents to a collection, as shown below:
db.collection.insertMany(
 [ <document 1> , <document 2>, ... ]
 )
Sample:
> db.FirstCol.insertMany([{name:"Mary Smith",sex:"Female",age:25,status:"A"},{name:"John White",sex:"Male",age:26,status:"B"},{name:"Michael White",sex:"Male",age:26,status:"A",groups:["news","sports"]}])
{

      "acknowledged" : true,
      "insertedIds" : [
              ObjectId("617282a3a4bb72d733b5c6d7"),
              ObjectId("617282a3a4bb72d733b5c6d8"),
              ObjectId("617282a3a4bb72d733b5c6d9")
      ]
}

Updating a Database

In MongoDB, you can use update() to update documents in a collection.
Update the data in the FirstCol collection where name is Mary Smith:
> db.FirstCol.update({name:"Mary Smith",sex:"Female",age:25,status:"A"},{$set:{'age':28}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
Show the result:
> db.FirstCol.find().pretty()
{
        "_id" : ObjectId("618904b6258a6c38daf13abd"),
        "name" : "Mary Smith",
        "sex" : "Female",
        "age" : 28,
        "status" : "A"
}
{
        "_id" : ObjectId("618904b6258a6c38daf13abe"),
        "name" : "John White",
        "sex" : "Male",
        "age" : 26,
        "status" : "B"
}
{
        "_id" : ObjectId("618904b6258a6c38daf13abf"),
        "name" : "Michael White",
        "sex" : "Male",
        "age" : 26,
        "status" : "A",
        "groups" : [
                "news",
                "sports"
        ]
}

Deleting a Database

In MongoDB, you can use remove() to delete documents from a collection, as shown below:
> db.FirstCol.remove({name:"Mary Smith",sex:"Female",age:28,status:"A"})
WriteResult({ "nRemoved" : 1 })
Show the result:
> db.FirstCol.find().pretty()
{
        "_id" : ObjectId("618904b6258a6c38daf13abe"),
        "name" : "John White",
        "sex" : "Male",
        "age" : 26,
        "status" : "B"
}
{
        "_id" : ObjectId("618904b6258a6c38daf13abf"),
        "name" : "Michael White",
        "sex" : "Male",
        "age" : 26,
        "status" : "A",
        "groups" : [
                "news",
                "sports"
        ]
}

References

For more information, see MongoDB official documentation.
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