如果所有键都作为字段存在，则在MongoDB中过滤文档？
为此，请使用$all，它将查找包含数组中所有元素（如“键”）的文档。首先让我们创建一个包含文档的集合-
> db.demo17.insertOne({"ListOfSubject":["MySQL","MongoDB","Java"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e13847255d0fc6657d21f0a")
}
> db.demo17.insertOne({"ListOfSubject":["C","Python","Java"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e13847e55d0fc6657d21f0b")
}
> db.demo17.insertOne({"ListOfSubject":["C++","MongoDB","PL/SQL"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e13849255d0fc6657d21f0c")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.demo17.find();
这将产生以下输出-
{ "_id" : ObjectId("5e13847255d0fc6657d21f0a"), "ListOfSubject" : [ "MySQL", "MongoDB", "Java" ] }
{ "_id" : ObjectId("5e13847e55d0fc6657d21f0b"), "ListOfSubject" : [ "C", "Python", "Java" ] }
{ "_id" : ObjectId("5e13849255d0fc6657d21f0c"), "ListOfSubject" : [ "C++", "MongoDB", "PL/SQL" ] }如果所有键都作为字段存在，这是用于过滤文档的查询-
> db.demo17.find({"ListOfSubject": { "$all": ["C++","PL/SQL","MongoDB"] } });这将产生以下输出-
{ "_id" : ObjectId("5e13849255d0fc6657d21f0c"), "ListOfSubject" : [ "C++", "MongoDB",
"PL/SQL" ] }