compiler: Sort models topologically

Sort models topologically using Base->Model as edges. This way
the base models are defined before the models extending them.

lib/compiler.js

@@ -1,6 +1,7 @@
 var assert = require('assert');
 var fs = require('fs');
 var path = require('path');
+var toposort = require('toposort');
 var ConfigLoader = require('./config-loader');
 var debug = require('debug')('loopback:boot:compiler');
 
@@ -176,15 +177,15 @@ function addAllBaseModels(registry, modelNames) {
 
   while (modelNames.length) {
     var name = modelNames.shift();
+
+    if (visited[name]) continue;
+    visited[name] = true;
     result.push(name);
 
     var definition = registry[name] && registry[name].definition;
     if (!definition) continue;
 
-    var base = definition.base || definition.options && definition.options.base;
-    if (!base || base in visited) continue;
-
-    visited[base] = true;
+    var base = getBaseModelName(definition);
 
     // ignore built-in models like User
     if (!registry[base]) continue;
@@ -195,9 +196,37 @@ function addAllBaseModels(registry, modelNames) {
   return result;
 }
 
+function getBaseModelName(modelDefinition) {
+  if (!modelDefinition)
+    return undefined;
+
+  return modelDefinition.base ||
+    modelDefinition.options && modelDefinition.options.base;
+}
+
 function sortByInheritance(instructions) {
-  // TODO implement topological sort
-  return instructions.reverse();
+  // create edges Base name -> Model name
+  var edges = instructions
+    .map(function(inst) {
+      return [getBaseModelName(inst.definition), inst.name];
+    });
+
+  var sortedNames = toposort(edges);
+
+  var instructionsByModelName = {};
+  instructions.forEach(function(inst) {
+    instructionsByModelName[inst.name] = inst;
+  });
+
+  return sortedNames
+    // convert to instructions
+    .map(function(name) {
+      return instructionsByModelName[name];
+    })
+    // remove built-in models
+    .filter(function(inst) {
+      return !!inst;
+    });
 }
 
 function findModelDefinitions(rootDir, sources) {

package.json

@@ -23,9 +23,10 @@
     "url": "https://github.com/strongloop/loopback-boot/blob/master/LICENSE"
   },
   "dependencies": {
-    "underscore": "^1.6.0",
+    "commondir": "0.0.1",
     "debug": "^0.8.1",
-    "commondir": "0.0.1"
+    "toposort": "^0.2.10",
+    "underscore": "^1.6.0"
   },
   "devDependencies": {
     "loopback": "^1.5.0",

test/compiler.test.js

@@ -359,6 +359,48 @@ describe('compiler', function() {
       var modelNames = instructions.models.map(getNameProperty);
       expect(modelNames).to.eql(['Car']);
     });
+
+    it('sorts models, base models first', function() {
+      appdir.createConfigFilesSync({}, {}, {
+        Vehicle: { dataSource: 'db' },
+        FlyingCar: { dataSource: 'db' },
+        Car: { dataSource: 'db' }
+      });
+      appdir.writeConfigFileSync('models/car.json', {
+        name: 'Car',
+        base: 'Vehicle'
+      });
+      appdir.writeConfigFileSync('models/vehicle.json', {
+        name: 'Vehicle'
+      });
+      appdir.writeConfigFileSync('models/flying-car.json', {
+        name: 'FlyingCar',
+        base: 'Car'
+      });
+
+      var instructions = boot.compile(appdir.PATH);
+
+      var modelNames = instructions.models.map(getNameProperty);
+      expect(modelNames).to.eql(['Vehicle', 'Car', 'FlyingCar']);
+    });
+
+    it('detects circular Model dependencies', function() {
+      appdir.createConfigFilesSync({}, {}, {
+        Vehicle: { dataSource: 'db' },
+        Car: { dataSource: 'db' }
+      });
+      appdir.writeConfigFileSync('models/car.json', {
+        name: 'Car',
+        base: 'Vehicle'
+      });
+      appdir.writeConfigFileSync('models/vehicle.json', {
+        name: 'Vehicle',
+        base: 'Car'
+      });
+
+      expect(function() { boot.compile(appdir.PATH); })
+        .to.throw(/cyclic dependency/i);
+    });
   });
 });