MongoDB聚合中如何使用$redact

$redact根据文档本身中存储的信息限制文档的内容。您可以在聚合中使用$cond和$redact。让我们创建一个文档集合-

> db.demo546.insertOne({"Value1":10,"Value2":20});{ "acknowledged" : true, "insertedId" : ObjectId("5e8e263f9e5f92834d7f05d7") } > db.demo546.insertOne({"Value1":40,"Value2":30,Value3:50});{ "acknowledged" : true, "insertedId" : ObjectId("5e8e26549e5f92834d7f05d8") } > db.demo546.insertOne({"Value1":100,"Value2":200,Value3:null});{ "acknowledged" : true, "insertedId" : ObjectId("5e8e26619e5f92834d7f05d9") } > db.demo546.insertOne({"Value1":400,"Value2":1000,Value3:null});{ "acknowledged" : true, "insertedId" : ObjectId("5e8e26e09e5f92834d7f05da") } > db.demo546.insertOne({"Value1":400,"Value2":200,Value3:null});{ "acknowledged" : true, "insertedId" : ObjectId("5e8e26f59e5f92834d7f05db") } > db.demo546.insertOne({"Value1":400,"Value2":1000,Value3:60});{ "acknowledged" : true, "insertedId" : ObjectId("5e8e27159e5f92834d7f05dc") }

在find()方法的帮助下显示集合中的所有文档-

> db.demo546.find();

这将产生以下输出-

{ "_id" : ObjectId("5e8e263f9e5f92834d7f05d7"), "Value1" : 10, "Value2" : 20 } { "_id" : ObjectId("5e8e26549e5f92834d7f05d8"), "Value1" : 40, "Value2" : 30, "Value3" : 50 } { "_id" : ObjectId("5e8e26619e5f92834d7f05d9"), "Value1" : 100, "Value2" : 200, "Value3" : null } { "_id" : ObjectId("5e8e26e09e5f92834d7f05da"), "Value1" : 400, "Value2" : 1000, "Value3" : null } { "_id" : ObjectId("5e8e26f59e5f92834d7f05db"), "Value1" : 400, "Value2" : 200, "Value3" : null } { "_id" : ObjectId("5e8e27159e5f92834d7f05dc"), "Value1" : 400, "Value2" : 1000, "Value3" : 60 }

以下是使用MongoDB聚合的$redact与$exists的查询-

> db.demo546.aggregate( { "$redact": { "$cond": { "if": { "$and": [ { "$lt": [ "$Value1", "$Value2" ] }, { "$ifNull": [ "$Value3", false ] } ] }, "then": "$$KEEP", "else": "$$PRUNE" } } } );

这将产生以下输出-

{ "_id" : ObjectId("5e8e27159e5f92834d7f05dc"), "Value1" : 400, "Value2" : 1000, "Value3" : 60 }