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[英]Entity Framework code first One to Many Relationship with same database table
[英]One to many relationship with junction table using Entity Framework code first
我首先使用EF6代码创建数据库,并努力使用联结表创建一对多关系。
这是我要执行的操作的一个示例:
Foo
实体可以包含任意数量(0-n)的Bar
实体,但是Bar
实体不一定属于Foo
。 我可能希望其他类型的实体也包含一个或多个Bar
,因此Bar
不包含其父级的外键很重要。
因此,联接表将如下所示:
Name | FooBar
------------|-------
Primary Key | BarID
Key | FooID
因此,如果我们按如下方式创建实体:
public class Foo
{
public long ID { get; set; }
public ICollection<Bar> Bars { get; set; }
}
public class Bar
{
public long ID { get; set; }
}
然后配置它们:
public class FooConfiguration : EntityTypeConfiguration<Foo>
{
HasKey(p => p.ID);
HasMany(p => p.Bars)
.WithRequired()
.Map(m => {
m.ToTable("FooBar");
m.MapKey("FooKey");
});
}
但这导致抛出以下异常:
An exception of type 'System.InvalidOperationException' occurred in mscorlib.dll but was not handled in user code. Additional information: The specified table 'FooBar' was not found in the model. Ensure that the table name has been correctly specified.
不幸的是,我不确定这意味着什么-我需要创建一个单独的FooBar
实体吗?
如何配置这些实体,以便正确创建联接表?
谢谢!
很抱歉要重新启用此线程,但是我想共享一个我创建的用于处理WebApi的实用程序,该实用程序具有许多这种类型的关系实例。 我们有多个业务对象,每个业务对象都与EventHistory,Messages,Files等相关,并且混乱地跟踪所有FluentAPI函数。 这是我想出的:
/// <summary>
/// Maps a many-to-many relationship that can only be navigated from TSource to TTarget.
/// </summary>
/// <typeparam name="TSource">Source type that can navigate to TTarget.</typeparam>
/// <typeparam name="TTarget">Target type that has no direct link back to TSource.</typeparam>
/// <param name="modelBuilder">An instance of DbModelBuilder</param>
/// <param name="expr">Lambda expression specifying the navigation property for this relationship from TSource to TTarget.</param>
/// <param name="leftKey">Optional argument to override the foreign key to TSource</param>
/// <param name="rightKey">Optional argument to override the foreign key to TTarget</param>
public static void MapDirectionalManyToMany<TSource, TTarget>(DbModelBuilder modelBuilder, Expression<Func<TSource, ICollection<TTarget>>> expr, string tableName = null, string leftKey = null, string rightKey = null)
where TSource : class
where TTarget : class {
modelBuilder.Entity<TSource>()
.HasMany(expr)
.WithMany()
.Map(m => {
m.MapLeftKey(leftKey ?? typeof(TSource).Name + "Id");
m.MapRightKey(rightKey ?? typeof(TTarget).Name + "Id");
m.ToTable(tableName ?? typeof(TSource).Name + typeof(TTarget).Name);
});
}
我这样应用这种关系:
ModelUtils.MapDirectionalManyToMany<MyResourceModel, SharedHistoryModel>(modelBuilder, x => x.History);
ModelUtils.MapDirectionalManyToMany<OtherResourceModel, SharedHistoryModel>(modelBuilder, x => x.History, "renamed_history");
如果您不想将foo
的键存储在bar
则必须进行多对多关系。 使它表现为一对多关系的方式取决于您的实现,仍然有一种方法可以确保bar
只有一个foo
,但是对于EF6来创建联结表,唯一的方法是许多关系。
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