$in¶
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- $in¶
The $in operator selects the documents where the value of a field equals any value in the specified array. To specify an $in expression, use the following prototype:
For comparison of different BSON type values, see the specified BSON comparison order.
{ field: { $in: [<value1>, <value2>, ... <valueN> ] } }
If the field holds an array, then the $in operator selects the documents whose field holds an array that contains at least one element that matches a value in the specified array (e.g. <value1>, <value2>, etc.)
在 2.6 版更改: MongoDB 2.6 removes the combinatorial limit for the $in operator that exists for earlier versions of the operator.
Examples¶
Use the $in Operator to Match Values¶
Consider the following example:
db.inventory.find( { qty: { $in: [ 5, 15 ] } } )
This query selects all documents in the inventory collection where the qty field value is either 5 or 15. Although you can express this query using the $or operator, choose the $in operator rather than the $or operator when performing equality checks on the same field.
Use the $in Operator to Match Values in an Array¶
The collection inventory contains documents that include the field tags, as in the following:
{ _id: 1, item: "abc", qty: 10, tags: [ "school", "clothing" ], sale: false }
Then, the following update() operation will set the sale field value to true where the tags field holds an array with at least one element matching either "appliances" or "school".
db.inventory.update(
{ tags: { $in: ["appliances", "school"] } },
{ $set: { sale:true } }
)
Use the $in Operator with a Regular Expression¶
The $in operator can specify matching values using regular expressions of the form /pattern/. You cannot use $regex operator expressions inside an $in.
Consider the following example:
db.inventory.find( { tags: { $in: [ /^be/, /^st/ ] } } )
This query selects all documents in the inventory collection where the tags field holds an array that contains at least one element that starts with either be or st.