实体框架代码优先 - 一个表/多个类型

Question

在我的数据库中,我创建了一个类似于这样的表:

dbo.Words
    WordId INT PRIMARY KEY
    WordText NVARCHAR(75)
    WordTypeId INT FK

WordTypeId引用另一个查找表.它将具有以下值之一:

Verb
Noun
Adjective

我想创建这样的实体类:

public class Word
{ ... }

public class Noun : Word
{ ... }

public class Verb : Word
{ ... }

public class WordType
{ ... }

public class MyContext : DbContext
{
    public DbSet<Noun> Nouns { get; set; }
    public DbSet<Verb> Verbs { get; set; }
    public DbSet<Word> Words { get; set; }
    public DbSet<WordType> WordTypes { get; set; }
}

我将如何在Entity Framework 4.1 - Code First中实现这一目标？当我查询名词DbSet时,我希望它只返回WordTypeId,而不是我的名词类型在WordTypes表中.

Answer 1

您需要采用每个层次结构表(TPH),其中整个层次结构映射到单个数据库表(dbo.Words),其中包含所有类的所有属性,并将该WordTypeId列用作Discriminator列.现在开始.

1.领域模型

public abstract class Word
{
    public int WordId { get; set; }
    public string WordText { get; set; }
    //DO NOT map the WordTypeId column
    //as it is used as the Discriminator column
}

public class Noun : Word { }
public class Verb : Word { }
public class Adjective : Word { }

2.背景

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    //Assuming WordTypeId eqauls 1 for Nouns, 2 for Verbs, 3 for Adjectives
    modelBuilder.Entity<Noun>().Map<Word>(c => c.Requires("WordTypeId").HasValue(1));
    modelBuilder.Entity<Verb>().Map<Word>(c => c.Requires("WordTypeId").HasValue(2));
    modelBuilder.Entity<Adjective>().Map<Word>(c => c.Requires("WordTypeId").HasValue(3));
}

要使用动词:

var verbs = x.Words.OfType<Verb>()