发布于 2015-09-14 15:08:35 | 83 次阅读 | 评论: 0 | 来源: 网络整理
Syntax: { field: { $type: <BSON type> } }
$type selects the documents where the value of the field is the specified BSON type.
Consider the following example:
db.inventory.find( { price: { $type : 1 } } )
This query will select all documents in the inventory collection where the price field value is a Double.
If the field holds an array, the $type operator performs the type check against the array elements and not the field.
Consider the following example where the tags field holds an array:
db.inventory.find( { tags: { $type : 4 } } )
This query will select all documents in the inventory collection where the tags array contains an element that is itself an array.
If instead you want to determine whether the tags field is an array type, use the $where operator:
db.inventory.find( { $where : "Array.isArray(this.tags)" } )
See the SERVER-1475 for more information about the array type.
Refer to the following table for the available BSON types and their corresponding numbers.
| Type | Number |
| Double | 1 |
| String | 2 |
| Object | 3 |
| Array | 4 |
| Binary data | 5 |
| Object id | 7 |
| Boolean | 8 |
| Date | 9 |
| Null | 10 |
| Regular Expression | 11 |
| JavaScript | 13 |
| Symbol | 14 |
| JavaScript (with scope) | 15 |
| 32-bit integer | 16 |
| Timestamp | 17 |
| 64-bit integer | 18 |
| Min key | 255 |
| Max key | 127 |
MinKey and MaxKey compare less than and greater than all other possible BSON element values, respectively, and exist primarily for internal use.
注解
To query if a field value is a MinKey, you must use the $type with -1 as in the following example:
db.collection.find( { field: { $type: -1 } } )
Example
Consider the following example operation sequence that demonstrates both type comparison and the special MinKey and MaxKey values:
db.test.insert( {x : 3});
db.test.insert( {x : 2.9} );
db.test.insert( {x : new Date()} );
db.test.insert( {x : true } );
db.test.insert( {x : MaxKey } )
db.test.insert( {x : MinKey } )
db.test.find().sort({x:1})
{ "_id" : ObjectId("4b04094b7c65b846e2090112"), "x" : { $minKey : 1 } }
{ "_id" : ObjectId("4b03155dce8de6586fb002c7"), "x" : 2.9 }
{ "_id" : ObjectId("4b03154cce8de6586fb002c6"), "x" : 3 }
{ "_id" : ObjectId("4b031566ce8de6586fb002c9"), "x" : true }
{ "_id" : ObjectId("4b031563ce8de6586fb002c8"), "x" : "Tue Jul 25 2012 18:42:03 GMT-0500 (EST)" }
{ "_id" : ObjectId("4b0409487c65b846e2090111"), "x" : { $maxKey : 1 } }
To query for the minimum value of a shard key of a sharded cluster, use the following operation when connected to the mongos:
use config
db.chunks.find( { "min.shardKey": { $type: -1 } } )
警告
Storing values of the different types in the same field in a collection is strongly discouraged.