检查 MongoDB 中是否存在该字段?
mongodbdatabasebig data analytics更新于 2026/1/13 6:37:17
您可以使用 $exists 运算符来实现此目的。首先，我们创建一个包含文档的集合。 −
>db.checkFieldExistsDemo.insertOne({"StudentFirstName":"John","StudentGender":"Male","StudentMongoDBScore":89});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd909611a844af18acdffbd")
}
>db.checkFieldExistsDemo.insertOne({"StudentFirstName":"Emma","StudentGender":"Female","StudentMongoDBScore":58});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd909781a844af18acdffbe")
}
>db.checkFieldExistsDemo.insertOne({"StudentFirstName":"Carol","StudentGender":"Male","StudentMongoDBScore":77});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd909871a844af18acdffbf")
}
>db.checkFieldExistsDemo.insertOne({"StudentFirstName":"David","StudentMongoDBScore":98});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd909a31a844af18acdffc0")
}
以下是使用 find() 方法显示集合中的所有文档的查询 −
> db.checkFieldExistsDemo.find().pretty();
这将产生以下输出 −
{
"_id" : ObjectId("5cd909611a844af18acdffbd"),
"StudentFirstName" : "John",
"StudentGender" : "Male",
"StudentMongoDBScore" : 89
}
{
"_id" : ObjectId("5cd909781a844af18acdffbe"),
"StudentFirstName" : "Emma",
"StudentGender" : "Female",
"StudentMongoDBScore" : 58
}
{
"_id" : ObjectId("5cd909871a844af18acdffbf"),
"StudentFirstName" : "Carol",
"StudentGender" : "Male",
"StudentMongoDBScore" : 77
}
{
"_id" : ObjectId("5cd909a31a844af18acdffc0"),
"StudentFirstName" : "David",
"StudentMongoDBScore" : 98
}
以下查询用于检查 MongoDB 中是否存在某个字段 −
> db.checkFieldExistsDemo.find({"StudentMongoDBScore":98, "StudentGender":{"$exists": false}},{'StudentFirstName': 1, '_id':0});
这将产生以下输出 −
{ "StudentFirstName" : "David" }
