如何以编程方式查询 DbContext 中的 DbSet？

Question

我正在尝试构建一个控制器，为我的所有查找表的编辑请求提供服务。我的 DbContext 上有几个从 IdNamePairBase 派生的 DbSet 变量，例如：

public DbSet<Country> Countries { get; set; } // Country derives from IdNamePairBase

如何将其中一个的名称传递给查询，以获取该列表中的所有项目？例如

var list = db.GetNamedDbSet("Countries");

然后，我需要从list 获得IEnumerable<IdNamePairBase> 以获得奖励积分。

Answer 1

如果表的名称与类型相对应，您可以在 DbContext 上使用 Set(Type type)。

 public IEnumerable<IdNamePairBase> GetNamedDbSet(string dbSetName)
 {
      var property = Type.GetType(dbSetName);
      if (property == null || !property.CanRead)
      {
         throw new ArgumentException("DbSet named " + dbSetName + " does not exist." );
      }

      // at this point you might want to check that the property is an enumerable type
      // and that the generic definition is convertible to IdNamePairBase by
      // inspecting the property type.  If you're sure that these hold, you could
      // omit the check.

      return Set(type).Cast<IdNamePairBase>();
 }

原答案

如果集合的名称与属性名称匹配，则可以使用反射。

 public IEnumerable<IdNamePairBase> GetNamedDbSet( string dbSetName )
 {
      var property = this.GetType().GetProperty( dbSetName );
      if (property == null || !property.CanRead)
      {
         throw new ArgumentException("DbSet named " + dbSetName + " does not exist." );
      }

      // at this point you might want to check that the property is an enumerable type
      // and that the generic definition is convertible to IdNamePairBase by
      // inspecting the property type.  If you're sure that these hold, you could
      // omit the check.

      var result = new List<IdNamePairBase>();
      foreach (var item in (IEnumerable)property.GetValue( this, null))
      {
          result.Add( (IdNamePairBase)item );
      }
      return result;
 }