在每次创建上下文时发出 DbContext.OnModelCreating

Emit DbContext.OnModelCreating on every context creation(在每次创建上下文时发出 DbContext.OnModelCreating)

问题描述

我首先使用实体​​框架代码来处理我的数据库.我有几个名称不同但结构相同的表，并且这些表动态出现在数据库中.我如何在运行时将 EntityFramework 映射到其中一个表并使用数据，就像我在 DbContext 的实体上工作一样?

I use entity framework code first to work with my database. I have several tables with different names but same structure, and this tables dynamically appears in database. How could I map EntityFramework to one of that tables at run-time and use data from just like I work this over entities of DbContext?

我为使它工作所做的工作:

What I've done to make it work:

例如，我的类描述动态创建表的结构是SetElement.

For example, my class what describes structure of dynamically created table is SetElement.

这是我的上下文:

public class DataContext : DbContext
{
    public DataContext()
        : base("RepositoryConnectionString") { }

    string setElementsTableId; // the name of table that need to be dynamicly mapped to 

    // Enforce model recreating
    public DataContext(string setElementsTableId)
        : this()
    {
        this.setElementsTableId = setElementsTableId;
    }


    /* some other entities */

    public DbSet<Entities.SetElement> SetElements { get; set; } // dynamicly mapped entity


    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        /* come configurations */

        if (!string.IsNullOrEmpty(setElementsTableId))
        {
            modelBuilder.Entity<Entities.SetElement>().Map(x => x.ToTable(setElementsTableId)); // map SetElements property to dynamicly created table
        }
    }
}

我如何使用它:

public static void AddSetElements(ICollection<SetElement> setElements, string tableId)
    {
     using (ctx = new DataContext(tableId)) // configere DataContext to map tableId table for entity SetElements
       try
       {
           var num = ctx.SetElements.Count();
           ctx.SetElements.AddRange(setElements);
           ctx.SaveChanges();
       }
       catch (Exception e)
       {
       }
 }

我还有一些方法可以从与 AddSetElements 相同的动态创建的表中获取、更新和删除数据.

I have also some methods to get, udtate and remove data from dynamicly created tables that are same to AddSetElements.

一切都如我所愿，但前提是 AddSetElements 首先运行，因为在第一个数据上下文创建 DbContext.OnModelCreating 运行并配置所有映射.但是下一个实例创建不会调用 DbContext.OnModelCreating.

All works just as I wish but only if AddSetElements runs first, because at the first datacontext creating DbContext.OnModelCreating runs and configure all mappings. But next instance creation doesn't call DbContext.OnModelCreating.

所以，我的问题是:如何在每次创建 DataContext 实例时调用 DbContext.OnModelCreating 然后我使用 DataContext(string setElementsTableId) 创建它?

So, my question is: how to call DbContext.OnModelCreating everytime of creating an instance of DataContext then I use DataContext(string setElementsTableId) to create it?

我知道，我的问题类似于EF 中的动态表映射"，但我在结果中一无所获.

I know, my question is similar to 'dynamic table mapping in EF' but I found nothing in the results.

顺便说一句.如果您知道另一种解决我的问题的方法，欢迎您.

By the way. If you know another way to solve my problem, you are welcome.

推荐答案

有一个内置功能可以解决您的问题:`IDbModelCacheKey;其实现将在您的配置中注册.关键是为您的不同上下文生成不同的密钥.

There is a built-in feature which may address your issue : `IDbModelCacheKey ; the implementation of which is to be registered in your configuration. The point is to generate a different key for your different contexts.

我会选择类似的东西:

一、配置

public class EntityFrameworkConfiguration: DbConfiguration
{
    public EntityFrameworkConfiguration()
    {
        this.SetModelCacheKey(ctx => new EntityModelCacheKey((ctx.GetType().FullName + ctx.Database.Connection.ConnectionString).GetHashCode()));
    }
}

然后是IDbModelCacheKey的实现

Then the implementation of the IDbModelCacheKey

public class EntityModelCacheKey : IDbModelCacheKey
{
    private readonly int _hashCode;

    public EntityModelCacheKey(int hashCode)
    {
        _hashCode = hashCode;
    }

    public override bool Equals(object other)
    {
        if (other == null) return false;
        return other.GetHashCode() == _hashCode;
    }

    public override int GetHashCode()
    {
        return _hashCode;
    }
}

最后，你的 DataContext

Finally, your DataContext

public class DataContext : DbContext
{

  string setElementsTableId; 

  // use the setElementsTableId as extended property of the 
  // connection string to generate a custom key
  public DataContext(string setElementsTableId)
        : base(ConfigurationManager.ConnectionStrings["RepositoryConnectionString"] 
 + "; Extended Properties="setElementsTableId=" + setElementsTableId + """)
  {
    this.setElementsTableId = setElementsTableId;
  }

  public DbSet<Entities.SetElement> SetElements { get; set; } 

  protected override void OnModelCreating(DbModelBuilder modelBuilder)
  {
    if (!string.IsNullOrEmpty(setElementsTableId))
    {
        modelBuilder.Entity<Entities.SetElement>().Map(x => x.ToTable(setElementsTableId)); 
    }
  }
}

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