映射许多关系与外键参考 [英] Mapping Many to Many Relationship w/ Foreign Key Reference
问题描述
我有以下架构（在我的头脑中）表格之间的关系如何。
[FooBar] [Foo] [Bar]
FooId PK，FK Id PK Id PK
BarId PK，FK BarId FK名称
IsRead名称描述
描述
虽然，当我尝试使用EF代码生成模式时，首先它不能解释实体之间的关系，因为我已经解释了它们（添加外键 FooId 到 [bar] 表），并且无法完全创建 [FooBar] 桥表
如果有人可以指导我如何使用EF4代码实现上述架构，我将不胜感激。无论解决方案涉及我的POCO模型的属性，流畅的配置或两者的混合都不重要 - 只要创建所需的数据库模式。
POCO模型：
public class Foo
{
public int Id {get;组; }
public string Text {get;组; }
public string描述{get;组; }
public int BarId {get;组; }
public Bar Bar {get;组; } / * bar entity * /
public virtual ICollection< Bar> BridgedBars {get;组; }
public Foo（）
{
Bars = new List< Bar>（）;
}
}
public class Bar
{
public int Id {get;组; }
public string Text {get;组; }
public string描述{get;组; }
public virtual ICollection< Foo> Fo子组; }
public virtual ICollection< Foo> BridgedFoos {get;组;
public Bar（）
{
Foos = new List&Foo>（）;
BridgedFoos = new List< Foo>（）;
}
}
public class FooBar
{
public int FooId {get;组; }
public int BarId {get;组; }
public virtual Foo Foo {get;组; }
public virtual Bar Bar {get;组; }
public bool IsRead {get;组; }
}
属于 Foo.BrideBars定义的关系 Bar 中的外键 FooId / code>。 EF不将此导航属性与 Bar 中的 ICollection< Foo> 属性之一相关联，因为有两个，EF不能唯一确定哪个是正确的对。因此，在另一端没有导航属性的 Foo.BrideBars 创建关系。可以这么说，有一个看不见的 Bar.Foo 属性导致外键。
数据库模式你想要映射到一个模型并不能真正代表多对多的关系，而是与中间的桥实体 FooBar 的两个一对多关系。您必须在导航属性中使用此类来定义正确的关系。它将如下所示：
public class Foo
{
public int Id {get;组; }
public string Text {get;组; }
public string描述{get;组; }
public int BarId {get;组; }
public Bar Bar {get;组; }
public virtual ICollection< FooBar> FooBars {get;组; }
}
public class Bar
{
public int Id {get;组; }
public string Text {get;组; }
public string描述{get;组; }
public virtual ICollection< Foo> Fo子组; }
public virtual ICollection< FooBar> FooBars {get;组;
public class FooBar
{
[Key，Column（Order = 0）]
public int FooId {get;组; }
[Key，Column（Order = 1）]
public int BarId {get;组; }
public virtual Foo Foo {get;组; }
public virtual Bar Bar {get;组; }
public bool IsRead {get;组; }
}
通过此模型中的命名约定将检测到正确的关系。只有 FooBar 实体，必须明确定义一个键，因为属性名称不符合约定（no Id 而没有 FooBarId 属性）。在这个模型中，使用 FooBar 中的复合键是有意义的。
我想，你真正的类和属性没有名字 Foo 和 Bar 。如果您的真实姓名不遵循约定，您可能必须指定与注释的关系 - 或使用Fluent API：
modelBuilder。实体< Foo>（）
.HasRequired（f => f.Bar）
.WithMany（b => b.Foos）
.HasForeignKey（f => f.BarId ）;
modelBuilder.Entity< FooBar>（）
.HasKey（fb => new {fb.FooId，fb.BarId}）; //取代[Key]注释
modelBuilder.Entity< FooBar>（）
.HasRequired（fb => fb.Foo）
.WithMany（f => f.FooBars）
.HasForeignKey（fb => fb.FooId）;
modelBuilder.Entity< FooBar>（）
.HasRequired（fb => fb.Bar）
.WithMany（b => b.FooBars）
.HasForeignKey（fb => fb.BarId）;
在您的数据库模式中， FooBar 有一个复合主键：
[FooBar] [Foo] [Bar]
FooId PK， FK Id PK Id PK
BarId PK，FK BarId FK名称
IsRead名称描述
描述
但是，在$ code> FooBar 中有一个PK是必要的，因为EF模型中的每个实体必须具有定义的键属性 - 单个或复合 - 映射到数据库表中的主键。
在此问题中 - 创建代码，许多到许多，在关联表中的附加字段 - 是如何处理这种类型的关系的更多细节。 （有时候，人们也称之为多对多关系有效负载（ IsRead 属性是您的示例模型中的有效负载） ，但事实上它不是很多对多。）
This should be a simple question for the well versed EF user.
I have the following schema (in my head) of how the relationships between the tables should look.
[FooBar] [Foo] [Bar]
FooId PK,FK Id PK Id PK
BarId PK,FK BarId FK Name
IsRead Name Description
Description
Though, when I try to generate the schema using EF code-first it fails to interpret the relationships between the entities as I've interpreted them (adds foreign key FooId to the [bar] table) and fails to fully create the [FooBar] bridge table.
If someone could guide me on how to achieve the above schema using EF4 code-first I'd appreciate it. Whether the solution involves attributes on my POCO models, fluent configurations or a hybrid of both doesn't matter much - as long as the desired database schema is created.
POCO Models:
public class Foo
{
public int Id { get; set; }
public string Text { get; set; }
public string Description { get; set; }
public int BarId { get; set; }
public Bar Bar { get; set; } /* bar entity */
public virtual ICollection<Bar> BridgedBars { get; set; }
public Foo()
{
Bars = new List<Bar>();
}
}
public class Bar
{
public int Id { get; set; }
public string Text { get; set; }
public string Description { get; set; }
public virtual ICollection<Foo> Foos { get; set; }
public virtual ICollection<Foo> BridgedFoos { get; set; }
public Bar()
{
Foos = new List<Foo>();
BridgedFoos = new List<Foo>();
}
}
public class FooBar
{
public int FooId { get; set; }
public int BarId { get; set; }
public virtual Foo Foo { get; set; }
public virtual Bar Bar { get; set; }
public bool IsRead { get; set; }
}
Your model will indeed create a foreign key FooId in the Bar which belongs to the relationship defined by Foo.BrideBars. EF doesn't relate this navigation property to one of the ICollection<Foo> properties in Bar because there are two of them and EF cannot determine uniquely which is the correct pair. As a result it creates a relationship for Foo.BrideBars without a navigation property on the other end. So to speak, there is an invisible Bar.Foo property which causes the foreign key.
The database schema you want to map to a model does not really represent a many-to-many relationship but instead two one-to-many relationships with the intermediate "bridge" entity FooBar. You must use this class in the navigation properties to define the correct relationships. It would look like this:
public class Foo
{
public int Id { get; set; }
public string Text { get; set; }
public string Description { get; set; }
public int BarId { get; set; }
public Bar Bar { get; set; }
public virtual ICollection<FooBar> FooBars { get; set; }
}
public class Bar
{
public int Id { get; set; }
public string Text { get; set; }
public string Description { get; set; }
public virtual ICollection<Foo> Foos { get; set; }
public virtual ICollection<FooBar> FooBars { get; set; }
}
public class FooBar
{
[Key, Column(Order = 0)]
public int FooId { get; set; }
[Key, Column(Order = 1)]
public int BarId { get; set; }
public virtual Foo Foo { get; set; }
public virtual Bar Bar { get; set; }
public bool IsRead { get; set; }
}
The correct relationships will be detected by naming conventions in this model. Only for the FooBar entity it is necessary to define a key explicitly because the property names do not meet the conventions (no Id and no FooBarId property). In this model it makes sense to use a composite key in FooBar.
I guess, your real classes and properties don't have the name Foo and Bar. If your real names do not follow the conventions you possibly have to specify the relationships with annotations - or with Fluent API:
modelBuilder.Entity<Foo>()
.HasRequired(f => f.Bar)
.WithMany(b => b.Foos)
.HasForeignKey(f => f.BarId);
modelBuilder.Entity<FooBar>()
.HasKey(fb => new { fb.FooId, fb.BarId }); // replaces the [Key] annotations
modelBuilder.Entity<FooBar>()
.HasRequired(fb => fb.Foo)
.WithMany(f => f.FooBars)
.HasForeignKey(fb => fb.FooId);
modelBuilder.Entity<FooBar>()
.HasRequired(fb => fb.Bar)
.WithMany(b => b.FooBars)
.HasForeignKey(fb => fb.BarId);
In your database schema the FooBar table will have a composite primary key:
[FooBar] [Foo] [Bar]
FooId PK,FK Id PK Id PK
BarId PK,FK BarId FK Name
IsRead Name Description
Description
But having a PK in FooBar is necessary because every entity in an EF model must have a key property defined - either single or composite - which maps to a primary key in the database table.
In this question - Create code first, many to many, with additional fields in association table - are more details how to work with such a type of relationship. (Sometimes people also call it "many-to-many relationship with payload" (the IsRead property is the "payload" in your example model), but in fact it's not many-to-many.)
这篇关于映射许多关系与外键参考的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
