如何检查MongoDB集合中的空白字段？
> db.demo485.insertOne({"FirstName":"Chris","LastName":""});{
"acknowledged" : true,
"insertedId" : ObjectId("5e82e9f6b0f3fa88e22790a8")
}
> db.demo485.insertOne({"FirstName":"David","LastName":"Miller"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e82e9fdb0f3fa88e22790a9")
}
> db.demo485.insertOne({"FirstName":"Chris","LastName":"Brown"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e82ea03b0f3fa88e22790aa")
}
> db.demo485.insertOne({"FirstName":"Robert","LastName":""});{
"acknowledged" : true,
"insertedId" : ObjectId("5e82ea0fb0f3fa88e22790ab")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo485.find();
这将产生以下输出-
{ "_id" : ObjectId("5e82e9f6b0f3fa88e22790a8"), "FirstName" : "Chris", "LastName" : "" }
{ "_id" : ObjectId("5e82e9fdb0f3fa88e22790a9"), "FirstName" : "David", "LastName" : "Miller" }
{ "_id" : ObjectId("5e82ea03b0f3fa88e22790aa"), "FirstName" : "Chris", "LastName" : "Brown"
}
{ "_id" : ObjectId("5e82ea0fb0f3fa88e22790ab"), "FirstName" : "Robert", "LastName" : "" }以下是检查空白字段的查询-
> db.demo485.find({"LastName" : {"$exists" : true, "$eq" : ""}})这将产生以下输出-
{ "_id" : ObjectId("5e82e9f6b0f3fa88e22790a8"), "FirstName" : "Chris", "LastName" : "" }
{ "_id" : ObjectId("5e82ea0fb0f3fa88e22790ab"), "FirstName" : "Robert", "LastName" : "" }