C#带有接口的泛型约束，用于解除API的耦合

本文关键字：用于 耦合 API 约束 接口 泛型 | 更新日期: 2023-09-27 18:13:15

在编写数据访问层时，我希望将面向公众的API与具体的数据库实现解耦。例如，假设我想使用MongoDb或Cassandra作为后备存储。

因此，我希望我的C#代码通过工厂方法等使用IThingDao。工厂将与实际实现相对应。

我有一些非常基本的接口和类示例来演示我希望实现的目标。不幸的是，这段代码生成了许多编译时错误，说这些类没有实现接口的成员。

以下定义了我的数据对象：

public interface IBase
{
    Object Id { get; set; }
    DateTime CreatedDate { get; set; }    
}
public interface IBaseMongoDb : IBase
{
    // Common MongoDb related things used by all concrete implementations
}
public interface IBaseCassandra : IBase
{
    // Common Cassandra related things used by all concrete implementations
}
public interface IThing : IBase
{
    String Name { get; set; }
}
public abstract class AbstractBase
{
    public virtual Object Id { get; set; }
    public DateTime CreatedDate { get; set; }
}
public abstract class AbstractMongoDbBase : AbstractBase
{
    [BsonId]
    public override Object Id { get; set; }
    // Other specific MongoDb stuff
}
public abstract class AbstractCassandraBase : AbstractBase
{
    // Cassandra related stuff
}
public class ThingMongoDbImpl : AbstractMongoDbBase, IThing, IBaseMongoDb
{
    public String Name { get; set; }
}
public class ThingCassandraImpl : AbstractCassandraBase, IThing, IBaseCassandra
{
    public String Name { get; set; }
}

MongoDb和Cassandra数据对象有单独的基本抽象，因为每个实现都有特定于一个和另一个的共同特性(如注释等(。

以下是数据访问接口：

public interface IDao<T>
{
    T Save( T a_Value );
    void Update( T a_Value );
    void Delete( T a_Value );
    T Find( Object a_Key );
}
public interface IThingDao : IDao<IThing>
{
    IThing FindByName( String a_Name );
}

以下是MongoDb和Cassandra的实现：

public abstract class AbstractMongoDbDao<T> where T : IBaseMongoDb, new()
{
    public T Save( T a_Value )
    {
        // Save
        return a_Value;
    }
    public void Update( T a_Value )
    {
        // Update
    }
    public void Delete( T a_Value )
    {
        // Delete
    }
    public T Find( Object a_Key )
    {
        return new T();
    }
}
public class ThingDaoMongoDbImpl : AbstractMongoDbDao<ThingMongoDbImpl>, IThingDao
{
    public IThing FindByName( String a_Name )
    {
        // Do the lookup and return value
        return new ThingMongoDbImpl();
    }
}

public abstract class AbstractCassandraDao<T> where T : IBaseCassandra, new()
{
    public T Save( T a_Value )
    {
        // Save
        return a_Value;
    }
    public void Update( T a_Value )
    {
        // Update
    }
    public void Delete( T a_Value )
    {
        // Delete
    }
    public T Find( Object a_Key )
    {
        return new T();
    }
}
public class ThingDaoCassandraImpl : AbstractCassandraDao<ThingCassandraImpl>, IThingDao
{
    public IThing FindByName( String a_Name )
    {
        // Do the lookup and return value
        return new ThingCassandraImpl();
    }
}

对于此代码，ThingDaoMongoDbImpl和ThingDaoCasandraImpl生成以下编译时错误：

Error   1   'generics.decouple.ThingDaoMongoDbImpl' does not implement interface member 'generics.decouple.IDao<generics.decouple.IThing>.Find(object)'. 'generics.decouple.AbstractMongoDbDao<generics.decouple.ThingMongoDbImpl>.Find(object)' cannot implement 'generics.decouple.IDao<generics.decouple.IThing>.Find(object)' because it does not have the matching return type of 'generics.decouple.IThing'.
Error   2   'generics.decouple.ThingDaoMongoDbImpl' does not implement interface member 'generics.decouple.IDao<generics.decouple.IThing>.Delete(generics.decouple.IThing)' C:'Projects'EDC'modules'EXCHANGES'CAD2CAD.Net'Z'Generics.cs 95  18  Z
Error   3   'generics.decouple.ThingDaoMongoDbImpl' does not implement interface member 'generics.decouple.IDao<generics.decouple.IThing>.Update(generics.decouple.IThing)' C:'Projects'EDC'modules'EXCHANGES'CAD2CAD.Net'Z'Generics.cs 95  18  Z
Error   4   'generics.decouple.ThingDaoMongoDbImpl' does not implement interface member 'generics.decouple.IDao<generics.decouple.IThing>.Save(generics.decouple.IThing)'   C:'Projects'EDC'modules'EXCHANGES'CAD2CAD.Net'Z'Generics.cs 95  18  Z
Error   5   'generics.decouple.ThingDaoCassandraImpl' does not implement interface member 'generics.decouple.IDao<generics.decouple.IThing>.Find(object)'. 'generics.decouple.AbstractCassandraDao<generics.decouple.ThingCassandraImpl>.Find(object)' cannot implement 'generics.decouple.IDao<generics.decouple.IThing>.Find(object)' because it does not have the matching return type of 'generics.decouple.IThing'.
Error   6   'generics.decouple.ThingDaoCassandraImpl' does not implement interface member 'generics.decouple.IDao<generics.decouple.IThing>.Delete(generics.decouple.IThing)'   C:'Projects'EDC'modules'EXCHANGES'CAD2CAD.Net'Z'Generics.cs 126 18  Z
Error   7   'generics.decouple.ThingDaoCassandraImpl' does not implement interface member 'generics.decouple.IDao<generics.decouple.IThing>.Update(generics.decouple.IThing)'   C:'Projects'EDC'modules'EXCHANGES'CAD2CAD.Net'Z'Generics.cs 126 18  Z
Error   8   'generics.decouple.ThingDaoCassandraImpl' does not implement interface member 'generics.decouple.IDao<generics.decouple.IThing>.Save(generics.decouple.IThing)' C:'Projects'EDC'modules'EXCHANGES'CAD2CAD.Net'Z'Generics.cs 126 18  Z

关于如何实现这一点，有什么建议吗？

感谢

C#带有接口的泛型约束，用于解除API的耦合

public class ThingDaoMongoDbImpl : AbstractMongoDbDao<ThingMongoDbImpl>, IThingDao
{
    public IThing FindByName( String a_Name )
    {
        // Do the lookup and return value
        return new ThingMongoDbImpl();
    }
     T Save( T a_Value ) { //implement it
     }
     void Update( T a_Value ) { 
     //implement it here
     }
     void Delete( T a_Value ) { // implement it here}
     T Find( Object a_Key ) { //implement it}
}

由于您没有实现IThingDao接口的方法，因此会出现编译时错误。你的public interface IThingDao : IDao<IThing>，从IDao扩展而来，所以你必须实现IDao<IThing>和的方法

更新

  public class ThingCassandraImpl : AbstractCassandraBase, IThing, IBaseCassandra, IThingDao
    {
        public String Name { get; set; }
        public IThing Save(IThing a_Value)
        {
            throw new NotImplementedException();
        }
        public void Update(IThing a_Value)
        {
            throw new NotImplementedException();
        }
        public void Delete(IThing a_Value)
        {
            throw new NotImplementedException();
        }
        public IThing Find(object a_Key)
        {
            throw new NotImplementedException();
        }
        public IThing FindByName(string a_Name)
        {
            throw new NotImplementedException();
        }
    }
    public abstract class AbstractCassandraDao<T> where T : IBaseCassandra,IThingDao, new() 
    {
        public T Save(T a_Value)
        {
            // Save
            return a_Value;
        }
        public void Update(T a_Value)
        {
            // Update
        }
        public void Delete(T a_Value)
        {
            // Delete
        }
        public T Find(Object a_Key)
        {
            return new T();
        }
    }
    public class ThingDaoCassandraImpl : AbstractCassandraDao<ThingCassandraImpl>
    {
        public IThing FindByName(String a_Name)
        {
            // Do the lookup and return value
            return new ThingCassandraImpl();
        }
        public IThing Save(IThing a_Value)
        {
            throw new NotImplementedException();
        }
        public void Update(IThing a_Value)
        {
            throw new NotImplementedException();
        }
        public void Delete(IThing a_Value)
        {
            throw new NotImplementedException();
        }
        public IThing Find(object a_Key)
        {
            throw new NotImplementedException();
        }
    }
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