c# - Linq thenBy() 抛出 "The best overloaded method match ThenBy() for has some invalid arguments"异常

Question

我有以下方法:

public List<LambdaExpression> defaultSortExpressions { get; set; }

private IQueryable<TEntity> orderEntries(IQueryable<TEntity> entries)
{
    var n = 0;
    foreach (var sortExpression in defaultSortExpressions)
    {
        if (n == 0)
        {
            entries = Queryable.OrderBy(entries, (dynamic)sortExpression);
        }
        else
        {
            entries = Queryable.ThenBy(entries, (dynamic)sortExpression);
        }
        n = n + 1;
    }
    return entries;
}

当执行 TheyBy() 行时，我收到以下异常:

"The best overloaded method match for 'System.Linq.Queryable.ThenBy(System.Linq.IOrderedQueryable, System.Linq.Expressions.Expression>)' has some invalid arguments"}
System.Exception {Microsoft.CSharp.RuntimeBinder.RuntimeBinderException

为什么这不起作用？

Answer 1

entries在编译时被强强制转换为 IQueryable<TEntity> ，而ThenBy需要 IOrderedQueryable<TEntity> 。您可以尝试类型转换 entries如IOrderedQueryable<TEntity>在将其传递给 ThenBy() 之前。或者您可以捕获调用 OrderBy 的结果在具有正确类型的单独变量中调用 ThenBy上。

private IQueryable<TEntity> orderEntries(IQueryable<TEntity> entries)
{
    if(defaultSortExpressions.Count == 0)
        return entries;        
    IOrderedQueryable<TEntity> ordered = Queryable.OrderBy(entries, (dynamic) defaultSortExpressions[0]);
    
    foreach (var sortExpression in defaultSortExpressions.Skip(1))
    {
        ordered = Queryable.ThenBy(ordered, (dynamic)sortExpression);            
    }
    return ordered;
}