SQLite3 :: ConstraintException：约束失败：

我正在尝试学习Ruby on Rails，并且遇到了需要帮助的问题。我想做的是使用表单创建项目经理，但是当我填写表单并单击提交后，显示以下错误：

I'm trying to learn Ruby on Rails and have encountered a problem I need help with. What I'm trying to do is to create a "project manager" with a form, but whne I'm filled in the form and clicks submit the following error is shown:

ActiveRecord::StatementInvalid in ProjectsController#create

SQLite3::ConstraintException: constraint failed: INSERT INTO "projects" ("created_at", "description", "end_date", "start_date", "title", "updated_at", "user_id") VALUES (?, ?, ?, ?, ?, ?, ?)

Rails.root: /Applications/XAMPP/xamppfiles/htdocs/IDV450-labb1

Application Trace | Framework Trace | Full Trace
app/controllers/projects_controller.rb:14:in `create'

项目负责人：

1.   class ProjectsController < ApplicationController
2.
3.      def index
4.        @projects = Project.all
5.      end
6.
7.      def new
8.        @project = Project.new
9.      end
10.
11.     def create
12.       @project = Project.new(params[:project].merge(:user_id => current_user.id))
13.
14.       if @project.save
15.         redirect_to projects_path
16.       else
17.         render :action => "new"
18.       end
19.     end
20.   end

项目模型：

class Project < ActiveRecord::Base
    has_and_belongs_to_many :users
    belongs_to :ticket

    attr_accessible :user_id, :title, :description, :start_date, :end_date
end

新项目的视图：

<%= form_for @project do |f| %>
    <div class="text_field">
        <%= f.label :title%>
        <%= f.text_field :title%>
    </div>
    <div class="text_field">
        <%= f.label :description%>
        <%= f.text_field :description%>
    </div>
    <div class="dropdown">
        <%= f.label :start_date%>
        <%= date_select :start_date, :startdate %>
    </div>
    <div class="dropdown">
        <%= f.label :end_date%>
        <%= date_select :end_date, :enddate %>
    </div>
    <div class="select">
        <%= f.label :title%>
    </div>
    <div class="submit">
        <%= f.submit "Save" %>
    </div>
<% end %>

数据库模型：

Project:
    - id: int
    - user_id: int
    - title: varchar(50)
    - description: varchar(500)
    - start_date: date
    - end_date: date
    - created_at: datetime
    - updated_at: datetime

请求发送的参数：

{"utf8"=>"✓",
 "authenticity_token"=>"CrFUjpsRCEWRprSmKtOk4nBxsxrwaII1WKLDWMQWuUI=",
 "project"=>{"title"=>"Foo project",
 "description"=>"A little description"},
 "start_date"=>{"start_date(1i)"=>"2013",
 "start_date(2i)"=>"2",
 "start_date(3i)"=>"7"},
 "end_date"=>{"end_date(1i)"=>"2014",
 "end_date(2i)"=>"3",
 "end_date(3i)"=>"12"},
 "commit"=>"Spara"}

它确实没有说出问题所在，但是在第14行发生它尝试保存到数据库。如果我在种子中创建一个项目，那么它将起作用！

It really doesn't say what the problem is, but it happens on line 14 when it tries to save to the db. If I create a project in seed it works!