Question

我有包含的Repository类。下面的代码适用于一对一的关系。但是对于收藏集，我需要将DbContext.Entry(model.Result).Reference(include).Load();更改为DbContext.Entry(model.Result).Collection(include).Load();

    public virtual async Task<TEntity> GetByIdAsync(object[] keyValues,
        List<Expression<Func<TEntity, object>>> includes,
        CancellationToken cancellationToken = default(CancellationToken))
    {
        var model = DbSet.FindAsync(keyValues, cancellationToken);
        if (includes == null) return await model;
        foreach (var include in includes)
            //if (include.Body.Type.IsAssignableFrom(typeof(ICollection<>)))
            DbContext.Entry(model.Result).Reference(include).Load();

        return await model;

        //return await DbSet.FindAsync(keyValues, cancellationToken);
    }

我可以在这里使用什么样的条件来分隔彼此的引用和集合？

谢谢。

编辑：示例对象是

System.Collections.Generic.IList`1 [[WestCore.Domain.Entities.WestLife.MhpProduct]]

通常，集合可以是ICollection或IList。

Answer 1

您可以使用更通用的Navigation方法，而不是单独的Reference / Collection方法。不幸的是，它没有lambda表达式的重载，所以你需要手动提取属性名称。由于您的方法设计不支持嵌套属性，您可以从lambda表达式主体获取该信息，强制转换为MemberExpression：

foreach (var include in includes)
{
    var propertyName = ((MemberExpression)include.Body).Member.Name;
    DbContext.Entry(model.Result).Navigation(propertyName).Load();
}

Answer 2

我改变它而不是明确地模仿FindByIdAsync我有一个稍微灵活的方法：

public async Task<T> GetItemAsync<T>(Expression<Func<T, bool>> filter, 
          List<Expression<Func<T,object>>> includes) where T: class
{
    var model = Set<T>();
    foreach (var include in includes)
    {
        model.Include(include);
    }
    return await model.FirstOrDefaultAsync(filter);
}

然后你打电话给：

var result = GetItemAsync<MyEntity>(x => x.Id == 3, 
             new List<Expression<Func<MyEntity, object>>> 
             { 
                 x => s.SomeProperty, 
                 x => s.SomeOtherProperty
             });

这与你的非常相似，但是更灵活一点，只会一次点击数据库，而不是懒得加载所有内容，就像我相信你现有的代码一样。这可能是你的意图，但我们没有这种背景。

另外 - 调用model.Result并使用非asyc Load()方法意味着您的代码不像它那样异步友好...

Answer 3

编辑：

我发现我仍然遇到问题。是

public virtual async Task<TEntity> GetByIdAsync(object[] keyValues,
        List<Expression<Func<TEntity, object>>> includes,
        CancellationToken cancellationToken = default(CancellationToken))
    {
        Task<TEntity> model = null;

        foreach (var include in includes)
        {
            if (include.Body.Type.GetInterface(nameof(IEnumerable<TEntity>)) != null)
            { //this part generates SQL Below
                await DbSet.Include(include).LoadAsync(cancellationToken);
                model = DbSet.FindAsync(keyValues, cancellationToken);
            }
            else //this part is working
            {
                var propertyName = ((MemberExpression)include.Body).Member.Name;
                model = DbSet.FindAsync(keyValues, cancellationToken);
                await DbContext.Entry(model.Result).Navigation(propertyName).LoadAsync(cancellationToken);
            }
        }

        if (model == null)
            model = DbSet.FindAsync(keyValues, cancellationToken);

        return await model;
    }

IEnumerable部分生成以下SQL：

SELECT＆＃34; product.MhpProducts＆＃34; .MP_MHP_ID，＆＃34; product.MhpProducts＆＃34; .MP_PRODUCT_ID，＆＃34; product.MhpProducts＆＃34; .MP_G_ORDER，＆＃34; product.MhpProducts＆＃34; .G_END_DATE，＆＃34; product.MhpProducts＆＃34; .G_INSERT_BY，＆＃34; product.MhpProducts＆＃34; .G_INSERT_DATE，＆＃34; product.MhpProducts＆＃34; .G_IS_DELETED，＆＃34;产品.MhPProducts＆＃34; .G_START_DATE，＆＃34; product.MhpProducts＆＃34;。＆＃34; MP_WEST_CORE._DOMAIN._ENTITIES._WEST_LIFE._MHP_PRODUCT＆＃34; 来自MHP_PRODUCT＆＃34; product.MhpProducts＆＃34; 内部联接（ SELECT＆＃34; product0＆＃34; .TP_ID 来自TREE_PRODUCT＆＃34; product0＆＃34; ）＆＃34; t＆＃34; ON＆＃34; product.MhpProducts＆＃34; .MP_PRODUCT_ID =＆＃34; t＆＃34; .TP_ID ORDER BY＆＃34; t＆＃34; .TP_ID

实体框架核心根据类的类型显式加载相关数据

3 个答案: