如何在 EF Core 2 中为 .ThenInclude 编写 Repository 方法 [英] How to write Repository method for .ThenInclude in EF Core 2

问题描述

我正在尝试为 Entity Framework Core 2.0 编写一个存储库方法，该方法可以使用 .ThenInclude 处理返回的子属性集合，但是我在使用第二个表达式时遇到了问题.这是 .Include 的一种工作方法，它将返回实体的子属性(您提供一个 lambda 列表).

I'm trying to write a repository method for Entity Framework Core 2.0 that can handle returning child collections of properties using .ThenInclude, but I'm having trouble with the second expression. Here is a working method for .Include, which will return child properties (you supply a list of lambdas) of your entity.

public T GetSingle(Expression<Func<T, bool>> predicate, params Expression<Func<T, object>>[] includeProperties)
{
    IQueryable<T> query = _context.Set<T>();
    foreach (var includeProperty in includeProperties)
    {
        query = query.Include(includeProperty);
    } 

    return query.Where(predicate).FirstOrDefault();
}

现在我尝试编写一个方法，该方法将采用两个表达式的元组并将它们输入到 .Include(a => a.someChild).ThenInclude(b => b.aChildOfSomeChild) 链中.这不是一个完美的解决方案，因为它只处理一个孩子的一个孩子，但这是一个开始.

Now here is my attempt at writing a method that will take a Tuple of two Expressions and feed those into a .Include(a => a.someChild).ThenInclude(b => b.aChildOfSomeChild) chain. This isn't a perfect solution because it only handles one child of a child, but it's a start.

public T GetSingle(Expression<Func<T, bool>> predicate, params Tuple<Expression<Func<T, object>>, Expression<Func<T, object>>>[] includeProperties)
{
    IQueryable<T> query = _context.Set<T>();
    foreach (var includeProperty in includeProperties)
    {
         query = query.Include(includeProperty.Item1).ThenInclude(includeProperty.Item2);              
    }

    return query.Where(predicate).FirstOrDefault();
}

Intellisense 返回一个错误，指出无法从用法推断类型，请尝试明确指定类型".我有一种感觉，这是因为 Item2 中的表达式需要归类为与 Item1 有某种关系，因为它需要知道它拥有的子关系.

Intellisense returns an error saying "The type cannot be inferred from the usage, try specifying the type explicitly". I have a feeling it's because the expression in Item2 needs to be classified as somehow related to Item1, because it needs to know about the child relationship it has.

编写这样的方法有什么想法或更好的技巧吗?

Any ideas or better techniques for writing a method like this?

推荐答案

我在网上找到了这个存储库方法，它完全符合我的要求.Yared 的回答很好，但并非完全如此.

I found this repository method online and it does exactly what I wanted. Yared's answer was good, but not all the way there.

/// <summary>
/// Gets the first or default entity based on a predicate, orderby delegate and include delegate. This method default no-tracking query.
/// </summary>
/// <param name="selector">The selector for projection.</param>
/// <param name="predicate">A function to test each element for a condition.</param>
/// <param name="orderBy">A function to order elements.</param>
/// <param name="include">A function to include navigation properties</param>
/// <param name="disableTracking"><c>True</c> to disable changing tracking; otherwise, <c>false</c>. Default to <c>true</c>.</param>
/// <returns>An <see cref="IPagedList{TEntity}"/> that contains elements that satisfy the condition specified by <paramref name="predicate"/>.</returns>
/// <remarks>This method default no-tracking query.</remarks>
public TResult GetFirstOrDefault<TResult>(Expression<Func<TEntity, TResult>> selector,
                                          Expression<Func<TEntity, bool>> predicate = null,
                                          Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
                                          Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>> include = null,
                                          bool disableTracking = true)
{
    IQueryable<TEntity> query = _dbSet;
    if (disableTracking)
    {
        query = query.AsNoTracking();
    }

    if (include != null)
    {
        query = include(query);
    }

    if (predicate != null)
    {
        query = query.Where(predicate);
    }

    if (orderBy != null)
    {
        return orderBy(query).Select(selector).FirstOrDefault();
    }
    else
    {
        return query.Select(selector).FirstOrDefault();
    }
}

用法:

var affiliate = await affiliateRepository.GetFirstOrDefaultAsync(
    predicate: b => b.Id == id,
    include: source => source
        .Include(a => a.Branches)
        .ThenInclude(a => a.Emails)
        .Include(a => a.Branches)
        .ThenInclude(a => a.Phones));

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