MongoDB查询代表不等于null还是空？
要将查询设置为不等于null或空，请使用$nin运算符。语法如下
db.yourCollectionName.find({yourFieldName:{$nin:[null,""]}});让我们创建包含文档的集合
> db.notEqualToNullOrEmptyDemo.insertOne({"UserName":"Larry","UserAge":24});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9d20b6a629b87623db1b26")
}
> db.notEqualToNullOrEmptyDemo.insertOne({"UserName":"","UserAge":29});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9d20bea629b87623db1b27")
}
> db.notEqualToNullOrEmptyDemo.insertOne({"UserName":"Sam","UserAge":32});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9d20c7a629b87623db1b28")
}
> db.notEqualToNullOrEmptyDemo.insertOne({"UserName":null,"UserAge":27});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9d20d2a629b87623db1b29")
}
> db.notEqualToNullOrEmptyDemo.insertOne({"UserName":"Robert","UserAge":26});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9d20dda629b87623db1b2a")
}
> db.notEqualToNullOrEmptyDemo.insertOne({"UserName":"","UserAge":23});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9d20e7a629b87623db1b2b")
}以下是在find()方法的帮助下显示集合中所有文档的查询
> db.notEqualToNullOrEmptyDemo.find().pretty();
这将产生以下输出
{
"_id" : ObjectId("5c9d20b6a629b87623db1b26"),
"UserName" : "Larry",
"UserAge" : 24
}
{
"_id" : ObjectId("5c9d20bea629b87623db1b27"),
"UserName" : "",
"UserAge" : 29
}
{
"_id" : ObjectId("5c9d20c7a629b87623db1b28"),
"UserName" : "Sam",
"UserAge" : 32
}
{
"_id" : ObjectId("5c9d20d2a629b87623db1b29"),
"UserName" : null,
"UserAge" : 27
}
{
"_id" : ObjectId("5c9d20dda629b87623db1b2a"),
"UserName" : "Robert",
"UserAge" : 26
}
{
"_id" : ObjectId("5c9d20e7a629b87623db1b2b"),
"UserName" : "",
"UserAge" : 23
}以下是将条件设置为不等于null或为空的查询
> db.notEqualToNullOrEmptyDemo.find({UserName:{$nin:[null,""]}}).pretty();这将产生以下输出
{
"_id" : ObjectId("5c9d20b6a629b87623db1b26"),
"UserName" : "Larry",
"UserAge" : 24
}
{
"_id" : ObjectId("5c9d20c7a629b87623db1b28"),
"UserName" : "Sam",
"UserAge" : 32
}
{
"_id" : ObjectId("5c9d20dda629b87623db1b2a"),
"UserName" : "Robert",
"UserAge" : 26
}