Added pre.save middleware that fixes tree after new node insertion

lib/nested_set.js

@@ -13,6 +13,53 @@ var NestedSetPlugin = function(schema, options) {
   schema.add({ rgt: {type: Number, min: 0} });
   schema.add({ parentId: {type: Schema.ObjectId} });
 
+  schema.pre('save', function(next) {
+    var self = this;
+    var model = mongoose.model(modelName);
+    if (self.parentId) {
+      self.parent(function(err, parentNode) {
+        if (!err && parentNode && parentNode.lft && parentNode.rgt) {
+
+          // find siblings and check if they have lft and rgt values set
+          self.siblings(function(err, nodes) {
+            if (nodes.every(function(node) { return node.lft && node.rgt;})) {
+              var maxRgt = 0;
+              nodes.forEach(function(node) {
+                if (node.rgt > maxRgt) {
+                  maxRgt = node.rgt;
+                }
+              });
+              if (nodes.length === 0) {
+                // if it is a leaf node, the maxRgt should be the lft value of the parent
+                maxRgt = parentNode.lft;
+              }
+              model.update({lft: { $gt: maxRgt}}, {$inc: {lft: 2}}, {multi: true}, function(err, updatedCount) {
+                model.update({rgt: { $gt: maxRgt}}, {$inc: {rgt: 2}}, {multi: true}, function(err, updatedCount2) {
+                  self.lft = maxRgt + 1;
+                  self.rgt = maxRgt + 2;
+                  next();
+                });
+              });
+            } else {
+              // the siblings do not have lft and rgt set. This means tree was not build.
+              // warn on console and move on.
+//              console.log('WARNING: tree is not built for ' + modelName + ' nodes. Siblings does not have lft/rgt');
+              next();
+            }
+          });
+        } else {
+          // parent node does not have lft and rgt set. This means tree was not built.
+          // warn on console and move on.
+//          console.log('WARNING: tree is not built for ' + modelName + ' nodes. Parent does not have lft/rgt');
+          next();
+        }
+      });
+    } else {
+      // no parentId is set, so ignore
+      next();
+    }
+  });
+
 
   // Builds the tree by populating lft and rgt using the parentIds
   schema.static('rebuildTree', function(parent, left, callback) {
@@ -61,6 +108,13 @@ var NestedSetPlugin = function(schema, options) {
     return self.lft < other.lft && other.lft < self.rgt;
   });
 
+  // returns the parent node
+  schema.method('parent', function(callback) {
+    var self = this;
+    var model = mongoose.model(modelName);
+    model.findOne({_id: self.parentId}, callback);
+  });
+
   // Returns the list of ancestors + current node
   schema.method('selfAndAncestors', function(callback) {
     var self = this;

tests/nested_set_test.js

@@ -167,6 +167,22 @@ var tests = testCase({
       });
     });
   },
+  'parent should return parent node': function(test) {
+    test.expect(4);
+    User.findOne({username: 'michael'}, function(err, user) {
+      User.rebuildTree(user, 1, function() {
+        User.findOne({username: 'kelly'}, function(err, kelly) {
+          test.ok(!err)
+          test.ok(kelly)
+          kelly.parent(function(err, node) {
+            test.ok(!err);
+            test.equal('meredith',node.username)
+            test.done()
+          });
+        });
+      });
+    });
+  },
   'selfAndAncestors should return all ancestors higher up in tree + current node': function(test) {
     test.expect(2);
     User.findOne({username: 'michael'}, function(err, user) {
@@ -344,6 +360,75 @@ var tests = testCase({
         });
       });
     });
+  },
+  'pre save middleware should not set lft and rgt if there is no parentId': function(test) {
+    test.expect(4);
+    var user = new User({
+      username: 'joe'
+    })
+    user.save(function(err, joe) {
+      test.ok(!err);
+      test.equal('joe', joe.username);
+      test.ok(!joe.lft);
+      test.ok(!joe.rgt);
+      test.done();
+    });
+  },
+  'adding a new leaf node the a built tree should re-arrange the tree correctly': function(test) {
+    test.expect(22)
+    User.findOne({username: 'michael'}, function(err, michael) {
+      User.rebuildTree(michael, 1, function() {
+        User.findOne({username: 'creed'}, function(err, creed) {
+          var newUser = new User({
+            username: 'joe',
+            parentId: creed._id
+          })
+          newUser.save(function(err, joe) {
+            User.find(function(err, users) {
+              // see docs/test_tree_after_leaf_insertion.png for the graphical representation of this tree 
+              // with lft/rgt values after the insertion
+              users.forEach(function(person) {
+                if (person.username === 'michael') {
+                  test.equal(1, person.lft);
+                  test.equal(22, person.rgt);
+                } else if (person.username === 'meredith') {
+                  test.equal(2, person.lft);
+                  test.equal(9, person.rgt);
+                } else if (person.username === 'jim') {
+                  test.equal(10, person.lft);
+                  test.equal(17, person.rgt);
+                } else if (person.username === 'angela') {
+                  test.equal(18, person.lft);
+                  test.equal(21, person.rgt);
+                } else if (person.username === 'kelly') {
+                  test.equal(3, person.lft);
+                  test.equal(4, person.rgt);
+                } else if (person.username === 'creed') {
+                  test.equal(5, person.lft);
+                  test.equal(8, person.rgt);
+                } else if (person.username === 'phyllis') {
+                  test.equal(11, person.lft);
+                  test.equal(12, person.rgt);
+                } else if (person.username === 'stanley') {
+                  test.equal(13, person.lft);
+                  test.equal(14, person.rgt);
+                } else if (person.username === 'dwight') {
+                  test.equal(15, person.lft);
+                  test.equal(16, person.rgt);
+                } else if (person.username === 'oscar') {
+                  test.equal(19, person.lft);
+                  test.equal(20, person.rgt);
+                } else if (person.username === 'joe') {
+                  test.equal(6, person.lft);
+                  test.equal(7, person.rgt);
+                }
+              });
+              test.done();
+            });
+          });
+        });
+      });
+    });
   }
 });