$mod¶
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$mod¶Select documents where the value of a field divided by a divisor has the specified remainder (i.e. perform a modulo operation to select documents). To specify a
$modexpression, use the following syntax:{ field: { $mod: [ divisor, remainder ] } } The
$modoperator errors when passed an array with fewer or more than two elements. See Not Enough Elements Error and Too Many Elements Error for details.
Examples¶
Use $mod to Select Documents¶
Consider a collection inventory with the following documents:
{ "_id" : 1, "item" : "abc123", "qty" : 0 } { "_id" : 2, "item" : "xyz123", "qty" : 5 } { "_id" : 3, "item" : "ijk123", "qty" : 12 }
Then, the following query selects those documents in the
inventory collection where value of the qty field modulo
4 equals 0:
db.inventory.find( { qty: { $mod: [ 4, 0 ] } } )
The query returns the following documents:
{ "_id" : 1, "item" : "abc123", "qty" : 0 } { "_id" : 3, "item" : "ijk123", "qty" : 12 }
Not Enough Elements Error¶
The $mod operator errors when passed an array with fewer than
two elements.
Array with Single Element¶
The following operation incorrectly passes the $mod operator
an array that contains a single element:
db.inventory.find( { qty: { $mod: [ 4 ] } } )
The statement results in the following error:
error: { "$err" : "bad query: BadValue malformed mod, not enough elements", "code" : 16810 }
Empty Array¶
The following operation incorrectly passes the $mod operator
an empty array:
db.inventory.find( { qty: { $mod: [ ] } } )
The statement results in the following error:
error: { "$err" : "bad query: BadValue malformed mod, not enough elements", "code" : 16810 }
Too Many Elements Error¶
The $mod operator errors when passed an array with more than
two elements.
For example, the following operation attempts to use the $mod
operator with an array that contains four elements:
error: { "$err" : "bad query: BadValue malformed mod, too many elements", "code" : 16810 }
Floating Point Arguments¶
The $mod expression rounds decimal input towards zero.
The following examples demonstrate this behavior:
Input query:
db.inventory.find( { qty: { $mod: [ 4.0, 0 ] } } )
Results:
{ _id: 1, item: 'abc123', qty: 0 } { _id: 3, item: 'ijk123', qty: 12 }
Input query:
db.inventory.find( { qty: { $mod: [ 4.5, 0 ] } } )
Results:
{ _id: 1, item: 'abc123', qty: 0 } { _id: 3, item: 'ijk123', qty: 12 }
Input query:
db.inventory.find( { qty: { $mod: [ 4.99, 0 ] } } )
Results:
{ _id: 1, item: 'abc123', qty: 0 } { _id: 3, item: 'ijk123', qty: 12 }
Each query applies 4 to the $mod expression regardless of
decimal points, resulting in the same result set.