MongoDB查询条件比较两个字段？
您可以使用$where运算符以及find()方法来比较MongoDB中的两个字段。语法如下：
db.yourCollectionName.find({$where:”yourCondition”}).pretty();为了理解上述语法，让我们创建包含一些文档的集合。用于创建包含文档的集合的查询如下：
>db.compareTwoFields.insert({"Id":1,"FullName":{"FirstName":"John","LastName":"Smith"},
"BranchName":"ComputerScience"});
WriteResult({ "nInserted" : 1 })
>db.compareTwoFields.insert({"Id":2,"FullName":{"FirstName":"Smith","LastName":"Smith"},
"BranchName":"Civil"});
WriteResult({ "nInserted" : 1 })
>db.compareTwoFields.insert({"Id":3,"FullName":{"FirstName":"David","LastName":"Smith"},
"BranchName":"Mechanical"});
WriteResult({ "nInserted" : 1 })现在，您可以借助find()method显示集合中的所有文档。查询如下：
> db.compareTwoFields.find().pretty();
以下是输出：
{
"_id" : ObjectId("5c6c237568174aae23f5ef64"),
"Id" : 1,
"FullName" : {
"FirstName" : "John",
"LastName" : "Smith"
},
"BranchName" : "ComputerScience"
}
{
"_id" : ObjectId("5c6c239868174aae23f5ef65"),
"Id" : 2,
"FullName" : {
"FirstName" : "Smith",
"LastName" : "Smith"
},
"BranchName" : "Civil"
}
{
"_id" : ObjectId("5c6c23b468174aae23f5ef66"),
"Id" : 3,
"FullName" : {
"FirstName" : "David",
"LastName" : "Smith"
},
"BranchName" : "Mechanical"
}以下是用于比较MongoDB中两个字段的查询：
>db.compareTwoFields.find({$where:"this.FullName.FirstName==this.FullName.LastName"}).
pretty();以下是输出：
{
"_id" : ObjectId("5c6c239868174aae23f5ef65"),
"Id" : 2,
"FullName" : {
"FirstName" : "Smith",
"LastName" : "Smith"
},
"BranchName" : "Civil"
}