db.update $min $max operators

README.md

@@ -432,7 +432,7 @@ db.count({}, function (err, count) {
 * `query` is the same kind of finding query you use with `find` and `findOne`
 * `update` specifies how the documents should be modified. It is either a new document or a set of modifiers (you cannot use both together, it doesn't make sense!)
   * A new document will replace the matched docs
-  * The modifiers create the fields they need to modify if they don't exist, and you can apply them to subdocs. Available field modifiers are `$set` to change a field's value, `$unset` to delete a field and `$inc` to increment a field's value. To work on arrays, you have `$push`, `$pop`, `$addToSet`, `$pull`, and the special `$each` and `$slice`. See examples below for the syntax.
+  * The modifiers create the fields they need to modify if they don't exist, and you can apply them to subdocs. Available field modifiers are `$set` to change a field's value, `$unset` to delete a field, `$inc` to increment a field's value and `$min`, `$max` to check if specified field is smaller or is greater than the current value of the field. To work on arrays, you have `$push`, `$pop`, `$addToSet`, `$pull`, and the special `$each` and `$slice`. See examples below for the syntax.
 * `options` is an object with two possible parameters
   * `multi` (defaults to `false`) which allows the modification of several documents if set to true
   * `upsert` (defaults to `false`) if you want to insert a new document corresponding to the `update` rules if your `query` doesn't match anything. If your `update` is a simple object with no modifiers, it is the inserted document. In the other case, the `query` is stripped from all operator recursively, and the `update` is applied to it.
@@ -540,6 +540,18 @@ db.update({ _id: 'id6' }, { $push: { fruits: { $each: ['banana', 'orange'] } } }
 db.update({ _id: 'id6' }, { $push: { fruits: { $each: ['banana'], $slice: 2 } } }, {}, function () {
   // Now the fruits array is ['apple', 'orange']
 });
+
+// Update the value of the field, only if specified field is smaller or greater than the current value of the field
+// Let's say the database contains this document
+// doc = { _id: 'id1', name: 'Name', value: 5 }
+// $min can be used to update field if current value is greater than the specified value 
+db.update({ _id: 'id1' }, { $min: { value: 2 } }, {}, function () {
+  // The document will be updated to { _id: 'id1', name: 'Name', value: 2 }
+});
+// $max can be used to update field if current value is smaller than the specified value 
+db.update({ _id: 'id1' }, { $max: { value: 8 } }, {}, function () {
+  // The document will be updated to { _id: 'id1', name: 'Name', value: 8 }
+});
 ```
 
 ### Removing documents

lib/model.js

@@ -386,6 +386,22 @@ lastStepModifierFunctions.$inc = function (obj, field, value) {
   }
 };
 
+/**
+ * Updates the value of the field, only if specified field is greater than the current value of the field
+ */
+lastStepModifierFunctions.$max = function (obj, field, value) {
+  if (typeof obj[field] === 'undefined') obj[field] = value;
+  else if (value > obj[field]) obj[field] = value;
+};
+
+/**
+ * Updates the value of the field, only if specified field is smaller than the current value of the field
+ */
+lastStepModifierFunctions.$min = function (obj, field, value) {
+  if (typeof obj[field] === 'undefined') obj[field] = value;
+  else if (value < obj[field]) obj[field] = value;
+};
+
 // Given its name, create the complete modifier function
 function createModifierFunction (modifier) {
   return function (obj, field, value) {

test/model.test.js

@@ -725,6 +725,78 @@ describe('Model', function () {
 
     });   // End of '$pull modifier'
 
+    describe('$max modifier', function () {
+      it('Will set the field to the updated value if value is greater than current one, without modifying the original object', function () {
+        var obj = { some:'thing', number: 10}
+            , updateQuery = {$max:{number:12}}
+            , modified = model.modify(obj,updateQuery);
+
+        modified.should.deep.equal({some:'thing',number:12});
+
+        obj.should.deep.equal({some:'thing', number:10});
+      });
+
+      it('Will not update the field if new value is smaller than current one', function () {
+        var obj = { some:'thing', number: 10}
+            , updateQuery = {$max:{number:9}}
+            , modified = model.modify(obj,updateQuery);
+
+        modified.should.deep.equal({some:'thing',number:10});
+      });
+
+      it('Will create the field if it does not exist', function () {
+        var obj = {some:'thing'}
+            , updateQuery = {$max:{number:10}}
+            , modified = model.modify(obj,updateQuery);
+
+        modified.should.deep.equal({some:'thing', number:10});
+      });
+
+      it('Works on embedded documents', function () {
+        var obj = {some:'thing', somethingElse:{number:10}}
+            , updateQuery = {$max:{'somethingElse.number':12}}
+            , modified = model.modify(obj,updateQuery);
+
+        modified.should.deep.equal({some:'thing',somethingElse:{number:12}});
+      });
+    });// End of '$max modifier'
+
+    describe('$min modifier', function () {
+      it('Will set the field to the updated value if value is smaller than current one, without modifying the original object', function () {
+        var obj = { some:'thing', number: 10}
+            , updateQuery = {$min:{number:8}}
+            , modified = model.modify(obj,updateQuery);
+
+        modified.should.deep.equal({some:'thing',number:8});
+
+        obj.should.deep.equal({some:'thing', number:10});
+      });
+
+      it('Will not update the field if new value is greater than current one', function () {
+        var obj = { some:'thing', number: 10}
+            , updateQuery = {$min:{number:12}}
+            , modified = model.modify(obj,updateQuery);
+
+        modified.should.deep.equal({some:'thing',number:10});
+      });
+
+      it('Will create the field if it does not exist', function () {
+        var obj = {some:'thing'}
+            , updateQuery = {$min:{number:10}}
+            , modified = model.modify(obj,updateQuery);
+
+        modified.should.deep.equal({some:'thing', number:10});
+      });
+
+      it('Works on embedded documents', function () {
+        var obj = {some:'thing', somethingElse:{number:10}}
+            , updateQuery = {$min:{'somethingElse.number':8}}
+            , modified = model.modify(obj,updateQuery);
+
+        modified.should.deep.equal({some:'thing',somethingElse:{number:8}});
+      });
+    });// End of '$min modifier'
+
   });   // ==== End of 'Modifying documents' ==== //