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Legal Studies我想在一个已经创建的文档中创建一个新字段。如何使用 MongoDB 查询来完成这项操作？
使用 $addToSet 在 MongoDB 中创建一个新字段。让我们首先使用文档创建集合 -
> db.createFieldDemo.insertOne({"StudentFirstName":"John","StudentAge":21});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd99e28b50a6c6dd317ad95")
}
> db.createFieldDemo.insertOne({"StudentFirstName":"Larry","StudentAge":23});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd99e2fb50a6c6dd317ad96")
}
> db.createFieldDemo.insertOne({"StudentFirstName":"Chris","StudentAge":22});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd99e38b50a6c6dd317ad97")
}
> db.createFieldDemo.insertOne({"StudentFirstName":"David","StudentAge":25});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd99e43b50a6c6dd317ad98")
}以下查询使用 find() 方法显示集合中的所有文档 -
> db.createFieldDemo.find().pretty();
这将生成以下输出 -
{
"_id" : ObjectId("5cd99e28b50a6c6dd317ad95"),
"StudentFirstName" : "John",
"StudentAge" : 21
}
{
"_id" : ObjectId("5cd99e2fb50a6c6dd317ad96"),
"StudentFirstName" : "Larry",
"StudentAge" : 23
}
{
"_id" : ObjectId("5cd99e38b50a6c6dd317ad97"),
"StudentFirstName" : "Chris",
"StudentAge" : 22
}
{
"_id" : ObjectId("5cd99e43b50a6c6dd317ad98"),
"StudentFirstName" : "David",
"StudentAge" : 25
}以下查询用于创建一个新字段。在此，我们创建一个字段“StudentLastName” -
> db.createFieldDemo.update({_id: ObjectId("5cd99e43b50a6c6dd317ad98")}, {$addToSet: {"StudentLastName": "Miller"}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })让我们检查上述集合中的所有文档 -
> db.createFieldDemo.find().pretty();
这将生成以下输出 -
{
"_id" : ObjectId("5cd99e28b50a6c6dd317ad95"),
"StudentFirstName" : "John",
"StudentAge" : 21
}
{
"_id" : ObjectId("5cd99e2fb50a6c6dd317ad96"),
"StudentFirstName" : "Larry",
"StudentAge" : 23
}
{
"_id" : ObjectId("5cd99e38b50a6c6dd317ad97"),
"StudentFirstName" : "Chris",
"StudentAge" : 22
}
{
"_id" : ObjectId("5cd99e43b50a6c6dd317ad98"),
"StudentFirstName" : "David",
"StudentAge" : 25,
"StudentLastName" : [
"Miller"
]
}
更新于： 30-Jul-2019
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