通用抽象构建器属性需要转换

Question

我构建了一个通用（抽象）构建器，它将提供基本实现对于将在测试期间使用的实体构建器。

这是实体库class:

public abstract class Entity : IObjectState
{
    [NotMapped]
    public ObjectState ObjectState { get; set; }
}

这是IKey接口:

public interface IKey
{
    int Id { get; set; }
}

这是 Builder class:

public abstract class Builder<T> where T : Entity, IKey, new()
{
    protected int _id { get; set; }
    protected ObjectState _objectState { get; set; }

    public Builder()
    {
        _objectState = ObjectState.Added;
    }

    public virtual Builder<T> WithId(int id)
    {
        this._id = id;
        return this;
    }

    public virtual Builder<T> HavingObjectState(ObjectState objectState)
    {
        _objectState = objectState;
        return this;
    }

    public static implicit operator T(Builder<T> builder)
    {
        return new T
        {
            Id = builder._id,
            ObjectState = builder._objectState
        };
    }
}

这是一个示例 UnitBuilder 实现：

public class UnitBuilder : Builder<Unit>
{
    private string _shortDescription;
    private string _longDescription;

    public UnitBuilder WithShort(string shortDescription)
    {
        _shortDescription = shortDescription;
        return this;
    }

    public UnitBuilder WithLong(string longDescription)
    {
        _longDescription = longDescription;
        return this;
    }

    public static implicit operator Unit(UnitBuilder builder)
    {
        return new Unit
        {
            Id = builder._id,
            ObjectState = builder._objectState,
            Short = builder._shortDescription,
            Long = builder._longDescription
        };
    }
}

这就是我遇到的问题：

错误：

Error CS1061 'Builder' does not contain a definition for 'WithShort' and no extension method 'WithShort' accepting a first argument of type 'Builder' could be found (are you missing a using directive or an assembly reference?)

我明白发生了什么，但我想要一个比 thirdUnit.

更好（更优雅）的解决方案

更新：

根据建议，我将以下内容添加到 UnitBuilder class:

public new UnitBuilder WithId(int id)
{
    return (UnitBuilder)base.WithId(id);
}

public new UnitBuilder WithObjectState(ObjectState objectState)
{
    return (UnitBuilder)base.WithObjectState(objectState);
}

但现在我在基地中看不到任何一点 class...这必须是 general generic base class 问题，其他人是怎么处理的？也许 thirdUnit 解决方案很优雅，但我只是很难理解它？ :)

Answer 1

答案很简单，您的基础 class 构建器方法必须最后调用，并且不能与更具体的构建器 class 链接，因为它 returns 是通用的。所以只需将您的代码更改为：

Unit secondUnit = new UnitBuilder()
    .WithShort("ShortDesc")
    .WithId(10);

就是这样！

Answer 2

这是我的最终解决方案：

public abstract class Builder<TEntity, TBuilder>
        where TEntity : Entity, IKey, new()
        where TBuilder : Builder<TEntity, TBuilder>, new()
{
    protected int _id { get; set; }
    protected ObjectState _objectState { get; set; }

    public Builder()
    {
        _objectState = ObjectState.Added;
    }

    public virtual Builder<TEntity, TBuilder> WithId(int id)
    {
        this._id = id;
        return this;
    }

    public virtual Builder<TEntity, TBuilder> WithObjectState(ObjectState objectState)
    {
        this._objectState = objectState;
        return this;
    }

    public static implicit operator TEntity(Builder<TEntity, TBuilder> builder)
    {
        return new TEntity
        {
            Id = builder._id,
            ObjectState = builder._objectState
        };
    }
}

通用抽象构建器属性需要转换

Generic abstract builder properties needs casting

c#

generics

builder

creation-pattern