feat(lucid): add support for findByOrFail

just like findOrFail, findByOrFail can also remove lots of clauses

src/Lucid/Model/index.js

@@ -554,6 +554,25 @@ class Model {
     return result
   }
 
+  /**
+   * find for a row using key/value pairs
+   * or fail by throwing an exception.
+   *
+   * @method findByOrFail
+   *
+   * @param  {String}     key
+   * @param  {Mixed}     value
+   *
+   * @return {Object}
+   */
+  static * findByOrFail (key, value) {
+    const result = yield this.findBy(key, value)
+    if (!result) {
+      throw new CE.ModelNotFoundException(`Unable to fetch results for ${key} ${value}`)
+    }
+    return result
+  }
+
   /**
    * returns all records for a given model
    *

test/unit/lucid.spec.js

@@ -820,6 +820,27 @@ describe('Lucid', function () {
       expect(user.username).to.equal('bea')
     })
 
+    it('should throw exception when unable to find a row using key/value pair', function * () {
+      class User extends Model {
+      }
+      try {
+        yield User.findByOrFail('username', 'koka')
+        expect(true).to.equal(false)
+      } catch (e) {
+        expect(e.name).to.equal('ModelNotFoundException')
+        expect(e.message).to.equal('Unable to fetch results for username koka')
+      }
+    })
+
+    it('should be able to find a given record using findByOrFail method', function * () {
+      class User extends Model {
+      }
+      yield User.query().insert({username: 'bea', firstname: 'Bea', lastname: 'Mine'})
+      let user = yield User.findByOrFail('username', 'bea')
+      expect(user instanceof User)
+      expect(user.username).to.equal('bea')
+    })
+
     it('should be able to find a given record using primary key', function * () {
       class User extends Model {
       }