如何解决因怪异的错误而导致的错误，包括 [英] How to resolve error with enitiy freamwork include

问题描述

我使用.Net 5和Entity Freamwork Core编写应用程序.我有正在寻找一些数据的方法.看起来像这样:

I write app using .Net 5 and Entity Freamwork Core. I have method that is looking for some data. It looks like this:

        public async Task<Result<List<Company>>> Search(string keyword, DateTime From, DateTime To, JobTitle jobTitle)
        {
            return Result.Ok(await _dataContext.Companies
                .Include(x => x.Employes
                    .WhereIf(From != default && To != default,
                        x => x.DateOfBirth >= From && x.DateOfBirth <= To && x.JobTitle == jobTitle))
                .WhereIf(!string.IsNullOrEmpty(keyword), 
                    x => x.Name.Contains(keyword))
                .ToListAsync());
        }

WhereIf看起来像这样:

WhereIf looks like this:

    public static class LinqExtension
    {
        public static IQueryable<TSource> WhereIf<TSource>(this IQueryable<TSource> source, bool condition, Expression<Func<TSource, bool>> predicate)
        {
            if (condition)
                return source.Where(predicate);

            return source;
        }

        public static IEnumerable<TSource> WhereIf<TSource>(this IEnumerable<TSource> source, bool condition, Func<TSource, bool> predicate)
        {
            if (condition)
                return source.Where(predicate);

            return source;
        }
    }

当我使用此方法时，出现此错误:

And when I use this method I got this error:

System.InvalidOperationException: The expression 'x.Employes.WhereIf(__p_0, x => (((x.DateOfBirth >= __From_1) AndAlso (x.DateOfBirth <= __To_2)) AndAlso (Convert(x.JobTitle, Int32) == Convert(__jobTitle_3, Int32))))' is invalid inside an 'Include' operation, since it does not represent a property access: 't => t.MyProperty'. To target navigations declared on derived types, use casting ('t => ((Derived)t).MyProperty') or the 'as' operator ('t => (t as Derived).MyProperty'). Collection navigation access can be filtered by composing Where, OrderBy(Descending), ThenBy(Descending), Skip or Take operations. For more information on including related data

如何解决此错误?

推荐答案

答案很简单.EF Core不会在 Include 定义中调用自定义方法.可以，因为此方法不是IQueryable方法.

Answer is simple. EF Core do not invoke custom methods in Include definition. Which is ok, because this method is not IQueryable method.

所以只需重写您的代码:

So just rewrite your code:

public async Task<Result<List<Company>>> Search(string keyword, DateTime From, DateTime To, JobTitle jobTitle)
{
   IQueryable<Company> query = _dataContext.Companies;
   if (From != default && To != default)
      query = query.Include(x => x.Employes
                 .Where(x => x.DateOfBirth >= From && x.DateOfBirth <= To && x.JobTitle == jobTitle));
   else
      query = query.Include(x => x.Employes);

   query = query.WhereIf(!string.IsNullOrEmpty(keyword), x => x.Name.Contains(keyword));

   return Result.Ok(await query.ToListAsync());
}

或者您可以将附加扩展名用于包含内容:

Or you can use additional extension for includes:

public static class LinqExtension
{
    public static IIncludableQueryable<TEntity, IEnumerable<TProp>> IncludeFiltered<TEntity, TProp>(
        this IQueryable<TEntity> source, bool condition, 
        Expression<Func<TEntity, IEnumerable<TProp>>> selector, 
        Expression<Func<TProp, bool>> predicate) 
        where TEntity : class
    {
        if (condition)
        {
            var newBody = Expression.Call(typeof(Enumerable), "Where", new[] {typeof(TProp)}, 
                selector.Body,
                predicate);

            selector = Expression.Lambda<Func<TEntity, IEnumerable<TProp>>>(newBody, selector.Parameters);
        }

        return source.Include(selector);
    }
}

public async Task<Result<List<Company>>> Search(string keyword, DateTime From, DateTime To, JobTitle jobTitle)
{
   return Result.Ok(await _dataContext.Companies
      .IncludeFiltered(From != default && To != default, 
         x => x.Employes, x => x.DateOfBirth >= From && x.DateOfBirth <= To && x.JobTitle == jobTitle)
      .WhereIf(!string.IsNullOrEmpty(keyword), 
         x => x.Name.Contains(keyword))
      .ToListAsync());
}

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