Can compare null and numbers

lib/model.js

@@ -130,6 +130,35 @@ function deepCopy (obj) {
 }
 
 
+/**
+ * Utility function for comparing things
+ * Assumes type checking was already done (a and b already have the same type)
+ */
+function compareNumbersAndStrings (a, b) {
+  if (a < b) { return -1; }
+  if (a > b) { return 1; }
+  return 0;
+}
+
+/**
+ * Compare things
+ * Things are defined as any native types (string, number, boolean, null, date) and objects
+ * In the case of objects and arrays, we compare the serialized versions
+ * If two objects dont have the same type, the (arbitrary) type hierarchy is: null, number, strings, dates, boolean, objects, arrays
+ * Return -1 if a < b, 1 if a > b and 0 if a = b (note that equality here is NOT the same as defined in areThingsEqual!)
+ */
+function compareThings (a, b) {
+  // null is less than everything except null
+  if (a === null) { return b === null ? 0 : -1; }
+  if (b === null) { return a === null ? 0 : 1; }
+
+  // Comparing numbers
+  if (typeof a === 'number') { return typeof b === 'number' ? compareNumbersAndStrings(a, b) : -1; }
+  if (typeof b === 'number') { return typeof a === 'number' ? compareNumbersAndStrings(a, b) : 1; }
+}
+
+
+
 // ==============================================================
 // Updating documents
 // ==============================================================
@@ -479,3 +508,4 @@ module.exports.modify = modify;
 module.exports.getDotValue = getDotValue;
 module.exports.match = match;
 module.exports.areThingsEqual = areThingsEqual;
+module.exports.compareThings = compareThings;

test/model.test.js

@@ -329,6 +329,39 @@ describe('Model', function () {
   });   // ==== End of 'Modifying documents' ==== //
 
 
+  describe.only('Comparing things', function () {
+
+    it('null is less than everything except null', function () {
+      var otherStuff = ["string", "", -1, 0, 5.3, 12, true, false, {}, { hello: 'world' }, [], ['quite', 5]];
+
+      model.compareThings(null, null).should.equal(0);
+
+      otherStuff.forEach(function (stuff) {
+        model.compareThings(null, stuff).should.equal(-1);
+        model.compareThings(stuff, null).should.equal(1);
+      });
+    });
+
+    it('After null, numbers are the smallest', function () {
+      var otherStuff = ["string", "", true, false, {}, { hello: 'world' }, [], ['quite', 5]]
+        , numbers = [-12, 0, 12, 5.7];
+
+      model.compareThings(-12, 0).should.equal(-1);
+      model.compareThings(0, -3).should.equal(1);
+      model.compareThings(5.7, 2).should.equal(1);
+      model.compareThings(5.7, 12.3).should.equal(-1);
+
+      otherStuff.forEach(function (stuff) {
+        numbers.forEach(function (number) {
+          model.compareThings(number, stuff).should.equal(-1);
+          model.compareThings(stuff, number).should.equal(1);
+        });
+      });
+    });
+
+  });   // ==== End of 'Comparing things' ==== //
+
+
   describe('Querying', function () {
 
     describe('Comparing things', function () {