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Reading/Writing Database

Last updated: 2022-03-17 20:19:51

    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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