如何检查MongoDB中的字段是[]还是{}？
要检查MongoDB中的字段是[]还是{}，可以使用以下语法-
db.yourCollectionName.find({
"yourOuterFieldName": { "$gt": {} },
"yourOuterFieldName.0": { "$exists": false }
});让我们首先创建包含文档的集合-
> db.checkFieldDemo.insert([
... { _id: 1010, StudentDetails: {} },
... { _id: 1011, StudentDetails: [ { StudentId: 1 } ] },
... { _id: 1012, StudentDetails: [ {} ] },
... { _id: 1013 },
... { _id: 1014, StudentDetails: null},
... { _id: 1015, StudentDetails: { StudentId: 1 } }
... ]);
BulkWriteResult({
"writeErrors" : [ ],
"writeConcernErrors" : [ ],
"nInserted" : 6,
"nUpserted" : 0,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"upserted" : [ ]
})以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.checkFieldDemo.find().pretty();
这将产生以下输出-
{ "_id" : 1010, "StudentDetails" : { } }
{ "_id" : 1011, "StudentDetails" : [ { "StudentId" : 1 } ] }
{ "_id" : 1012, "StudentDetails" : [ { } ] }
{ "_id" : 1013 }
{ "_id" : 1014, "StudentDetails" : null }
{ "_id" : 1015, "StudentDetails" : { "StudentId" : 1 } }以下是检查MongoDB中的字段是[]还是{}的查询-
> db.checkFieldDemo.find({
... "StudentDetails": { "$gt": {} },
... "StudentDetails.0": { "$exists": false }
... });这将产生以下输出-
{ "_id" : 1015, "StudentDetails" : { "StudentId" : 1 } }