MongoDB中如何连接条件

要在MongoDB中连接条件，请使用$cond，然后在其中使用$concat。让我们创建一个包含文档的集合-

> db.demo745.insertOne({Value1:"100",Value2:"100"}); { "acknowledged" : true, "insertedId" : ObjectId("5eae6419a930c785c834e554") } > db.demo745.insertOne({Value1:"40",Value2:"50"}); { "acknowledged" : true, "insertedId" : ObjectId("5eae6421a930c785c834e555") } > db.demo745.insertOne({Value1:"13",Value2:"45"}); { "acknowledged" : true, "insertedId" : ObjectId("5eae6429a930c785c834e556") }

在find()方法的帮助下显示集合中的所有文档-

> db.demo745.find();

这将产生以下输出-

{ "_id" : ObjectId("5eae6419a930c785c834e554"), "Value1" : "100", "Value2" : "100" } { "_id" : ObjectId("5eae6421a930c785c834e555"), "Value1" : "40", "Value2" : "50" } { "_id" : ObjectId("5eae6429a930c785c834e556"), "Value1" : "13", "Value2" : "45" }

以下是要与条件连接的查询-

> db.demo745.aggregate( ... [ ... { "$redact": { ... "$cond": [ ... { "$eq": [ ... { "$concat": [ "$Value1","$Value2" ] }, ... "1345" ... ]}, ... "$$KEEP", ... "$$PRUNE" ... ] ... }} ... ] ... )

这将产生以下输出-

{ "_id" : ObjectId("5eae6429a930c785c834e556"), "Value1" : "13", "Value2" : "45" }