如何在 MongoDB 查找查询中添加静态值字段?
mongodbdatabasebig data analytics
您可以将 $literal 运算符与聚合框架结合使用。首先，我们创建一个包含文档的集合。−
> db.fieldWithStaticValue.insertOne({"Name":"Larry","Age":24});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd6554c7924bb85b3f48948")
}
> db.fieldWithStaticValue.insertOne({"Name":"Chris","Age":23});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd655567924bb85b3f48949")
}
> db.fieldWithStaticValue.insertOne({"Name":"David","Age":26});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd655607924bb85b3f4894a")
}
以下是使用 find() 方法显示集合中的所有文档的查询 −
> db.fieldWithStaticValue.find();
这将产生以下输出 −
{ "_id" : ObjectId("5cd6554c7924bb85b3f48948"), "Name" : "Larry", "Age" : 24 }
{ "_id" : ObjectId("5cd655567924bb85b3f48949"), "Name" : "Chris", "Age" : 23 }
{ "_id" : ObjectId("5cd655607924bb85b3f4894a"), "Name" : "David", "Age" : 26 }
以下是使用 $literal 向 MongoDB 添加具有静态值的字段的查询 −
> db.fieldWithStaticValue.aggregate( [
{
$project: { Name: 1,Age:1, "StaticValue": { $literal: 100 } }
}
]);
这将产生以下输出 −
{ "_id" : ObjectId("5cd6554c7924bb85b3f48948"), "Name" : "Larry", "Age" : 24, "StaticValue" : 100 }
{ "_id" : ObjectId("5cd655567924bb85b3f48949"), "Name" : "Chris", "Age" : 23, "StaticValue" : 100 }
{ "_id" : ObjectId("5cd655607924bb85b3f4894a"), "Name" : "David", "Age" : 26, "StaticValue" : 100 }
