与实体框架状态模式 [英] State Pattern with Entity Framework

问题描述

我有一个模型查询，它可以是两种状态（有更多，但是本作的目的，我只是比较两个）：新和关闭。调查是在国家依赖于用户能够与询问该怎么办。例如封闭询问不能删除，其中作为一个新的调查能够被删除，等等（基本实施例）。

I have a model Enquiry, which can be in one of two states (there are more but for the purposes of this I will just compare two): New and Closed. The state the enquiry is in is dependant upon what a user is able to do with an enquiry. For example a closed enquiry cannot be deleted where as a new enquiry is able to be deleted and so forth (basic example).

我想用实体框架但不知道如何坚持这一点。下面是我的code。

I am wanting to persist this with Entity Framework but not sure how. Below is my code.

查询：

public class Enquiry
{
    public int Id { get; set; }
    public string CustomerAccountNumber { get; set; }

    public EnquiryState CurrentState { get; set; }
    public bool CanAddLines { get { return CurrentState.CanAddLines; } }
    public bool CanDelete { get { return CurrentState.CanDelete; } }

    public void ChangeState(EnquiryState currentState)
    {
        CurrentState = currentState;
    }

    public void CloseEnquiry()
    {
        CurrentState.CloseEnquiry();
    }

    /* More methods to change state here */

    public Enquiry()
    {
        CurrentState = new NewEnquiryState(this);
    }
}

EnquiryState：

EnquiryState:

public abstract class EnquiryState
{
    internal readonly Enquiry CurrentEnquiry;

    protected EnquiryState(Enquiry currentEnquiry)
    {
        CurrentEnquiry = currentEnquiry;
    }

    public virtual bool CanDelete
    {
        get { return false; }
    }

    public virtual bool CanAddLines
    {
        get { return false; }
    }

    /* More properties here */

    public abstract void CloseEnquiry();

    /* More states here */
}

NewEnquiryState：

NewEnquiryState:

public class NewEnquiryState : EnquiryState
{
    public NewEnquiryState(Enquiry enquiry) : base(enquiry) { }

    public override bool CanDelete
    {
        get { return true; }
    }

    public override bool CanAddLines
    {
        get { return true; }
    }

    /* ... */

    public override void CloseEnquiry()
    {
        CurrentEnquiry.ChangeState(new CloseEnquiryState(CurrentEnquiry));
    }

    /* ... */
}

CloseEnquiryState：

CloseEnquiryState:

public class CloseEnquiryState : EnquiryState
{
    public CloseEnquiryState(Enquiry enquiry) : base(enquiry) { }

    public override bool CanAddLines
    {
        get { return false; }
    }
    public override bool CanDelete
    {
        get { return false; }
    }

    /* ... */

    public override void CloseEnquiry()
    {
        throw new Exception("Closed Enquiry can't be closed");
    }
}

所以我的问题是，我不知道如何将这些不同的状态存储在数据库中，我应该使用每个国家的某种 INT 字段并将其映射在查询通过FK？另外，我需要的字段 CanAddLines 和 CanDelete 太映射到数据库？看到作为逻辑包含在国家内部，很新的状态模式范例

So my question is, I'm not sure how to store these different states in a database, should I use some sort of int field on each state and map them to the Enquiry via an FK? Also, do I need to map the fields CanAddLines and CanDelete to a database too? Seeing as the logic is contained within the state, quite new to the state pattern paradigm

推荐答案

要存储在您的国家不具有任何数据。所以，实际上你需要存储唯一的国家类型：

Your state does not have any data to be stored. So, actually you need to store only state type:

[NotMapped]
public EnquiryState CurrentState { get; set; }

public int StateType
{
    get 
    {
       // get value based on CurrentState
       return (CurrentState is NewEnquiryState) ? 0 : 1;
    }
    set
    {
        // create EnquireState based on value
        CurrentState = value == 0 ? 
            (EnquiryState)new NewEnquiryState(this) : 
            (EnquiryState)new CloseEnquiryState(this);
    }
}

BTW你不需要重写抽象类的虚拟成员，如果他们已经返回你所需要的（如 CanAddLines 和 CanDelete 属性 CloseEnquiryState ）

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