在EF代码首先计算列 [英] Calculated column in EF Code First

问题描述

我需要通过数据库（行的总和）来计算我的数据库有一列 - （rowsb的总和）。我使用的代码，第一个模型的创建数据库

I need to have one column in my database calculated by database as (sum of rows) - (sum of rowsb). I'm using code-first model to create my database.

下面是我的意思是：

public class Income {
      [Key]
      public int UserID { get; set; }
      public double inSum { get; set; }
}

public class Outcome {
      [Key]
      public int UserID { get; set; }
      public double outSum { get; set; }
}

public class FirstTable {
      [Key]
      public int UserID { get; set; }
      public double Sum { get; set; } 
      // This needs to be calculated by DB as 
      // ( Select sum(inSum) FROM Income WHERE UserID = this.UserID) 
      // - (Select sum(outSum) FROM Outcome WHERE UserID = this.UserID)
}

我怎么能在EF CodeFirst实现这一目标？

How can I achieve this in EF CodeFirst?

推荐答案

您可以创建的计算列的数据库中的表。在EF模型，你只是标注与 DatabaseGenerated 属性对应的属性：

You can create computed columns in your database tables. In the EF model you just annotate the corresponding properties with the DatabaseGenerated attribute:

[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
public double Summ { get; private set; } 

或用流利的映射：

modelBuilder.Entity<Income>().Property(t => t.Summ)
    .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Computed)

的建议通过 Matija葛契奇并在评论，这是一个好主意，使财产私人组，因为你可能永远都不想将其设置为应用程序代码。实体框架与私营制定者没有任何问题。

As suggested by Matija Grcic and in a comment, it's a good idea to make the property private set, because you'd probably never want to set it in application code. Entity Framework has no problems with private setters.

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