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" }