代码之家 › 专栏 › 技术社区 › bytebender

列表<object>。包含表达式树

lambda linq c#

bytebender · 技术社区 · 16 年前

我想建立一个表达式,将等同于预期的。。。

Expression<Func<ReferencedEntity, bool>> expected = (ReferencedEntity referencedEntity) => foreignKeys.Contains(referencedEntity.Id);
Expression<Func<ReferencedEntity, bool>> actual;

foreignKeys类型是一个 List<object>

这是我到目前为止所做的,我认为它将使用Expression.Call()方法,但不确定具体如何进行。

ParameterExpression entityParameter = Expression.Parameter(typeof(TReferencedEntity), "referencedEntity");
MemberExpression memberExpression = Expression.Property(entityParameter, "Id");
Expression convertExpression = Expression.Convert(memberExpression, typeof(object)); //This is becuase the memberExpression for Id returns a int.

//Expression containsExpression = Expression.Call(????

//actual = Expression.Lambda<Func<TReferencedEntity, bool>>(????, entityParameter);

谢谢你的帮助。

2 回复 | 直到 16 年前

bytebender 16 年前

    /// <summary>
    /// 
    /// </summary>
    /// <param name="foreignKeys"></param>
    /// <returns></returns>
    private Expression<Func<TReferencedEntity, bool>> BuildForeignKeysContainsPredicate(List<object> foreignKeys, string primaryKey)
    {
        Expression<Func<TReferencedEntity, bool>> result = default(Expression<Func<TReferencedEntity, bool>>);

        try
        {
            ParameterExpression entityParameter = Expression.Parameter(typeof(TReferencedEntity), "referencedEntity");
            ConstantExpression foreignKeysParameter = Expression.Constant(foreignKeys, typeof(List<object>));
            MemberExpression memberExpression = Expression.Property(entityParameter, primaryKey);
            Expression convertExpression = Expression.Convert(memberExpression, typeof(object));
            MethodCallExpression containsExpression = Expression.Call(foreignKeysParameter
                , "Contains", new Type[] { }, convertExpression);

            result = Expression.Lambda<Func<TReferencedEntity, bool>>(containsExpression, entityParameter);

        }
        catch (Exception ex)
        {
            throw ex;
        }

        return result;
    }