ER图 - 项目，任务和员工 [英] ER diagram - Project, Task and Employee

问题描述

更新：
公司可以有多个项目，公司也有员工。员工只能有一个公司，一个项目也只能有一家公司。
一个项目有几个任务。
在这些任务中，员工只能被分配到某些任务。

UPDATE: Company can have multiple Projects and Company also have Employees. An employee can only have one Company and a Project can also have only one company. A project has several tasks. Out of these tasks, an Employee will only be assigned to some of the tasks.

员工只能为项目分配任务，他/她是分配给。

The employee can only be assigned tasks for project that he/she is assigned to.

请查看以下内容，并帮助我如何创建数据库设计和最终实体模型
更新图基于两个评论：
如果这个ER图看起来不错，可以提供如何创建EF 4.1实体类的指导，尤其是对于EmployeeProjectTasks表。 我是EF 4.1 Code First的新手，想要创建这些课程的方向

Please review the following and help on how I should create the database design and the final entity model UPDATED DIAGRAM based on the two comments: If this ER diagram looks good, could you please provide guidance on how the EF 4.1 entity classes should be created, especially for EmployeeProjectTasks table. I am new to EF 4.1 Code First and would like some direction with creating these classes

如果此ER图看起来不正确，请推荐修订。

If this ER diagram looks incorrect, please recommend revisions.

推荐答案

员工只能为他/她分配到的项目分配任务。

The employee can only be assigned tasks for project that he/she is assigned to.

您的ER模型不执行此操作。

Your ER model doesn't enforce that.

这是因为 Project 和 Task ，所以在$ {code> EmployeeProjectTask.ProjectID ProjectID 的传播c>仅引用 EmployeeProject （但不是任务）。

That's because of the non-identifying relationship between Project and Task, so the propagation of ProjectID is cut-off in that branch of the diamond-shaped dependency and EmployeeProjectTask.ProjectID only references EmployeeProject (but not Task).

确保 EmployeeProjectTask 的模型与 EmployeeProject 和任务从相同的 项目将如下所示：

The model that ensures EmployeeProjectTask is connected with EmployeeProject and Task from the same Project would look like this:

注意任务是否具有复合PK {ProjectID，TaskNo} 以及项目.ProjectID 沿着钻石底部的分支和合并进行传播（导致 EmployeeProjectTask.ProjectID ，FK都包含 EmployeeProject 和 Task ）。

Note how Task has a composite PK {ProjectID, TaskNo}, and how Project.ProjectID is propagated down both "branches", and merged at the bottom of the "diamond" (resulting in the EmployeeProjectTask.ProjectID, with FK to both EmployeeProject and Task).

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