c# - '参数 'f' 未绑定(bind)到指定的 LINQ to Entities 查询表达式'

Question

使用 EF 6。有人可以告诉我我做错了什么吗？

public List<SearchResult> SearchDocuments(List<SearchCriteria> searchCriterias)
{
    List<SearchResult> results = new List<SearchResult>();
    var fieldSettings = LoadCoordinateSystemFieldSettings(searchCriterias);
    using (var context = CreateContext())
    {
        var tractsQuery = PredicateBuilder.False<v_UploadByTract_ActiveUploads>();
        foreach (var searchCriteria in searchCriterias)
        {
            var queryBuilder = PredicateBuilder.True<v_UploadByTract_ActiveUploads>();

            // tractsQuery
            if (searchCriteria.StateAPI.HasValue)
                queryBuilder = queryBuilder.And(a => a.StateAPI == searchCriteria.StateAPI.Value);
            if (searchCriteria.CountyAPI.HasValue)
                queryBuilder = queryBuilder.And(a => a.CountyAPI == searchCriteria.CountyAPI.Value);

            // ...
            // ... many more similar IF-ANDs
            // ...

            tractsQuery = tractsQuery.Or(queryBuilder);
        }

        var searchQuery = context.v_UploadByTract_ActiveUploads.AsExpandable().Where(tractsQuery).ToList();
        //.Select(a => SearchResult.Create(a));
        //results.AddRange(searchQuery.ToList());
    }

    return results;
}

public static class PredicateBuilder
{
    public static Expression<Func<T, bool>> True<T>() { return f => true; }
    public static Expression<Func<T, bool>> False<T>() { return f => false; }

    public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,
                                                        Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
        return Expression.Lambda<Func<T, bool>>
              (Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
    }

    public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1,
                                                         Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
        return Expression.Lambda<Func<T, bool>>
              (Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
    }
}

Answer 1

quetzalcoatl 感谢您的回答。另一个帖子做到了。从其他地方我遇到了 AsExpandable() 并忽略了这个认为它在谈论相同的东西。阅读您的帖子并重新阅读讨论后，这很有效。由于您的帖子显示为“评论”，因此我无法将其标记为答案。关于如何巩固那些讨厌的 IF 的任何建议。

C# PredicateBuilder Entities: The parameter 'f' was not bound in the specified LINQ to Entities query expression