每个层次结构的实体框架表未创建区分符 [英] Entity Framework Table per Hierarchy not creating Discriminator

问题描述

几次迁移后，我创建了一个继承层次结构.现在，当我使用代码优先迁移来更新数据库时，代码优先不会自动创建鉴别字段.此后，我删除了表并重新创建了它(使用代码优先迁移)，但没有任何运气.我唯一能想到的是，派生类中没有其他非虚拟"属性-创建继承结构是为了强制执行业务规则，该规则仅允许某些派生类型与另一个实体有关系./p>

基本类型:

 公共抽象类Process{私有ICollection< ProcessSpecification>_specifications {获取；放;}受保护的Process(){_specifications =新的List< ProcessSpecification>();}公共Int32 ID {放;}public String Description {get;放;}公共Int32 ToolId {放;}公共虚拟工具工具{放;}公共虚拟ICollection< ProcessSpecification>规格{得到{return _specifications;}设置{_specifications =值；}}} 

派生类(没有不同/唯一的标量属性):

 公共类AssemblyProcess:过程{私有ICollection< AssemblyProcessComponent>_组件;公共AssemblyProcess(){_components = new List< AssemblyProcessComponent>();}公共虚拟ICollection< AssemblyProcessComponent>组件{得到{return _components;}设置{_components =值;}}} 

另一种派生类型

 公共类MachiningProcess:过程{私有ICollection< MachiningProcessFeature>_特征;公共MachiningProcess(){_features = new List< MachiningProcessFeature>();}公共虚拟ICollection< MachiningProcessFeature>功能{取得{return _features;}设置{_features =值；}}} 

代码优先是否未在数据库中添加discriminator列，因为它看不到派生类之间的任何区别(因为没有任何唯一的非虚拟"属性)?如果是这样，我该如何解决?如果不是，为什么代码优先将不会在数据库中自动创建区分符列的原因有哪些?我还有另一个TPH结构，可以按照预期的方式工作.

DbContext:

  public LineProcessPlanningContext():base("LineProcessPlanning"){}公共DbSet< Component>组件{get;放;}公共DbSet< Customer>客户{放;}公共DbSet< Feature>功能{放;}公共DbSet< OperationDefinition>OperationDefinitions {放;}公共DbSet< PartDesign>零件设计{放;}公共DbSet< Process>流程{get;放;}公共DbSet< ProcessPlan>ProcessPlans {获取；放;}公共DbSet< ProcessPlanStep>ProcessPlanSteps {放;}公共DbSet< ProductionLine>生产线{get;放;}公共DbSet< StationCycleDefinition>StationCycleDefinitions {get;放;}公共DbSet< StationCycleStep>StationCycleSteps {放;}公共DbSet< StationDefinition>StationDefinitions {放;}公共DbSet< UnitOfMeasurement>UnitsOfMeasurement {get;放;}公共DbSet< Tool>工具{get;放;} 

我还尝试创建每种派生类型所独有的虚拟"属性.代码迁移将新属性作为列添加到表中，但是迁移未创建区分项列.

解决方案

在我的情况下，我发现了造成这种情况的原因，与您的情况相同.基类是 abstract ，因此EF不会为该类创建TPH表，因为它无法实例化.作为抽象基类的结果，EF将为每个派生类创建表，因此不需要区分列.

就我而言，从基类中删除抽象是可以接受的.一旦完成此操作，EF的TPH就会按预期工作.

I created an inheritance hierarchy after a few migrations. Now when I update the database using code first migrations, code-first is not automatically creating the discriminator field. I have since dropped the table and recreated it (using code-first migrations) without any luck. The only thing I can think of is that there are no additional "non-virtual" properties in the derived classes--the inheritance structure was created to enforce a business rule that only a certain derived type can have a relationship with another entity.

Base Type:

public abstract class Process
{

    private ICollection<ProcessSpecification> _specifications { get; set; }

    protected Process()
    {
        _specifications = new List<ProcessSpecification>();
    }        

    public Int32 Id { get; set; }
    public String Description { get; set; }
    public Int32 ToolId { get; set; }

    public virtual Tool Tool { get; set; }        
    public virtual ICollection<ProcessSpecification> Specifications
    {
        get { return _specifications; }
        set { _specifications = value; }
    }

}

Derived class (no different/unique scalar properties):

public class AssemblyProcess : Process
{
    private ICollection<AssemblyProcessComponent> _components;

    public AssemblyProcess()
    {
        _components = new List<AssemblyProcessComponent>();            
    }

    public virtual ICollection<AssemblyProcessComponent> Components
    {
        get { return _components; }
        set { _components = value; }
    }
}

Another derived type

public class MachiningProcess : Process
{
    private ICollection<MachiningProcessFeature> _features;

    public MachiningProcess()
    {
        _features = new List<MachiningProcessFeature>();
    }

    public virtual ICollection<MachiningProcessFeature> Features { get { return _features; } set { _features = value; } }
}

Is code-first not adding the discriminator column in the database because it doesn't see any differences between the derived classes (because of there not being any unique "non-virtual" properties)? If so, how do I get around this? If not, what are some reasons why code-first would not automatically create the discriminator column in the database? I have another TPH structure that works exactly the way it's supposed to.

DbContext:

public LineProcessPlanningContext()
        : base("LineProcessPlanning")
    {
    }   

public DbSet<Component> Components { get; set; }
public DbSet<Customer> Customers { get; set; }
public DbSet<Feature> Features { get; set; }
public DbSet<OperationDefinition> OperationDefinitions { get; set; }
public DbSet<PartDesign> PartDesigns { get; set; }
public DbSet<Process> Processes { get; set; }
public DbSet<ProcessPlan> ProcessPlans { get; set; }
public DbSet<ProcessPlanStep> ProcessPlanSteps { get; set; }
public DbSet<ProductionLine> ProductionLines { get; set; }       
public DbSet<StationCycleDefinition> StationCycleDefinitions { get; set; }
public DbSet<StationCycleStep> StationCycleSteps { get; set; }
public DbSet<StationDefinition> StationDefinitions { get; set; }
public DbSet<UnitOfMeasurement> UnitsOfMeasurement { get; set; }        
public DbSet<Tool> Tools { get; set; }

I also tried creating "dummy" properties that are unique to each derived type. Code migrations added the new properties as columns to the table, but the migration did not create a discriminator column.

解决方案

I figured out the cause of this in my situation, same as yours. The base class is abstract, therefore EF won't create a TPH table for that class since it can't be instantiated. As a result of the abstract base class, EF will create tables for each of the derived classes, and therefore no need for a discriminator column.

In my case, it was acceptable to remove abstract from the base class. Once I did this, EF's TPH worked as expected.

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