MongoDB中的$type操作符用于匹配字段值的数据类型。它可以在查询语句中使用,以便过滤特定类型的文档。以下是$type操作符的详细说明和举例:
语法:
{ field: { $type: <BSON type> } }
举例: 假设有以下集合,用于存储用户信息:
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1d"), "name" : "Alice", "age" : 25, "email" : "alice@example.com" }
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1e"), "name" : "Bob", "age" : "30", "email" : "bob@example.com" }
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1f"), "name" : "Charlie", "age" : null, "email" : "charlie@example.com" }
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b20"), "name" : "Dave", "age" : [25, 30], "email" : "dave@example.com" }
1.匹配字符串类型的字段值
db.users.find({ age: { $type: "string" } })
输出结果:
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1e"), "name" : "Bob", "age" : "30", "email" : "bob@example.com" }
2.匹配空值类型的字段值
db.users.find({ age: { $type: "null" } })
输出结果:
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1f"), "name" : "Charlie", "age" : null, "email" : "charlie@example.com" }
3.匹配数组类型的字段值
db.users.find({ age: { $type: "array" } })
输出结果:
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b20"), "name" : "Dave", "age" : [25, 30], "email" : "dave@example.com" }
4.匹配所有非空值类型的字段值
db.users.find({ age: { $type: { $not: "null" } } })
输出结果:
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1d"), "name" : "Alice", "age" : 25, "email" : "alice@example.com" }
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1e"), "name" : "Bob", "age" : "30", "email" : "bob@example.com" }
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b20"), "name" : "Dave", "age" : [25, 30], "email" : "dave@example.com" }
5.匹配所有数字类型的字段值
db.users.find({ age: { $type: "number" } })
输出结果:
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1d"), "name" : "Alice", "age" : 25, "email" : "alice@example.com" }
6.匹配所有布尔类型的字段值
db.users.find({ age: { $type: "bool" } })
输出结果:
# 没有匹配结果
7.匹配所有日期类型的字段值
db.users.find({ age: { $type: "date" } })
输出结果:
# 没有匹配结果
8.匹配所有objectId类型的字段值
db.users.find({ _id: { $type: "objectId" } })
输出结果:
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1d"), "name" : "Alice", "age" : 25, "email" : "alice@example.com" }
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1e"), "name" : "Bob", "age" : "30", "email" : "bob@example.com" }
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1f"), "name" : "Charlie", "age" : null, "email" : "charlie@example.com" }
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b20"), "name" : "Dave", "age" : [25, 30], "email" : "dave@example.com" }
9.匹配所有null类型和数字类型的字段值
db.users.find({ age: { $type: [ "null", "number" ] } })
输出结果:
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1d"), "name" : "Alice", "age" : 25, "email" : "alice@example.com" }
{ "_id" : ObjectId("61e02700c4b4e4d7717f2b1f"), "name" : "Charlie", "age" : null, "email" : "charlie@example.com" }
需要注意的是,$type操作符匹配的是BSON类型而非JavaScript类型,所以它与JavaScript类型之间存在一些差异。例如,JavaScript中的null类型在MongoDB中对应的是BSON的null类型,而JavaScript中的数组类型在MongoDB中对应的是BSON的array类型。因此,在使用$type操作符时需要了解BSON类型的定义和区别。