在对其中一个执行操作时，如何在MongoDB中比较两个字段？
要比较两个字段，请在MongoDB中使用$where。首先让我们创建一个包含文档的集合-
> db.demo7.insertOne({"FirstName1":"JOHN","FirstName2":"John"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e0ccd1a25ddae1f53b6222f")
}
> db.demo7.insertOne({"FirstName1":"Carol","FirstName2":"Mike"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e0ccd2725ddae1f53b62230")
}
> db.demo7.insertOne({"FirstName1":"bob","FirstName2":"BOB"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e0ccd3225ddae1f53b62231")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.demo7.find();
这将产生以下输出-
{ "_id" : ObjectId("5e0ccd1a25ddae1f53b6222f"), "FirstName1" : "JOHN", "FirstName2" : "John" }
{ "_id" : ObjectId("5e0ccd2725ddae1f53b62230"), "FirstName1" : "Carol", "FirstName2" : "Mike" }
{ "_id" : ObjectId("5e0ccd3225ddae1f53b62231"), "FirstName1" : "bob", "FirstName2" : "BOB" }这是在对两个字段之一执行操作时比较两个字段的查询-
> db.demo7.find({$where: "this.FirstName1.toLowerCase() == this.FirstName2.toLowerCase()"});这将产生以下输出-
{ "_id" : ObjectId("5e0ccd1a25ddae1f53b6222f"), "FirstName1" : "JOHN", "FirstName2" : "John" }
{ "_id" : ObjectId("5e0ccd3225ddae1f53b62231"), "FirstName1" : "bob", "FirstName2" : "BOB" }