MongoDB查询以根据是非值来查找
要基于真值或假值进行查找，请在find()中使用$exists。对于同一任务，您还需要点符号。
首先让我们创建一个包含文档的集合-
> db.demo367.insertOne(
... { "Id" : "102",
... "details" : [ { "Name" : "David"},
... { "Age" : 23, "CountryName" : "UK"} ],
... "isMarried" : false }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e57e0b62ae06a1609a00ae8")
}
> db.demo367.insertOne(
... { "Id" : "101",
... "details" : [ { "Name" : "Chris", "Subject" : [ "MySQL" ] },
... { "Age" : 21, "CountryName" : "US"} ],
... "isMarried" : true }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e57e0be2ae06a1609a00ae9")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo367.find();
这将产生以下输出-
{
"_id" : ObjectId("5e57e0b62ae06a1609a00ae8"), "Id" : "102", "details" : [
{ "Name" : "David" }, { "Age" : 23, "CountryName" : "UK" } ], "isMarried" : false }
{
"_id" : ObjectId("5e57e0be2ae06a1609a00ae9"), "Id" : "101", "details" : [
{ "Name" : "Chris", "Subject" : [ "MySQL" ] }, { "Age" : 21, "CountryName" : "US" } ], "isMarried" : true
}以下是通过与$exists进行检查以基于真假值查找的查询-
> db.demo367.find({"details.Subject": { $exists: false}});这将产生以下输出-
{ "_id" : ObjectId("5e57e0b62ae06a1609a00ae8"), "Id" : "102", "details" : [ { "Name" : "David" }, { "Age" : 23, "CountryName" : "UK" } ], "isMarried" : false }