计算列在EF代码第一 [英] Calculated column in EF Code First

问题描述

我需要在数据库中将一列数据库计算为（行总和） - （行数之和）。我正在使用代码优先模型来创建我的数据库。

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.

这是我的意思：

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)
}

如何在EF CodeFirst ？

How can I achieve this in EF CodeFirst?

推荐答案

您可以创建计算列在您的数据库表中。在EF模型中，您只需使用 DatabaseGenerated 属性注释相应的属性：

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; } 

或使用流畅的映射：

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

根据 Matija Grcic 的建议，评论，这是一个好主意，使财产私人集，因为你可能永远不想在应用程序代码中设置它。实体框架与私有设置者无关。

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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