c# - 扩展方法 & LINQ to Entities 无法识别方法错误

Question

在尝试将实体映射到 DTO 时，出现以下错误。

LINQ to Entities does not recognize the method 'Dto.Team ToTeamDto(Team, System.String)' method, and this method cannot be translated into a store expression."

这是查询

 bool includeTeam = true;

 var source = from c in db.Standings
                         where c.LeagueID == leagueId
                         select new Standing
                         {
                             id = c.StandingsId,
                             team = includeTeam ? c.Team.ToTeamDto("en-US") : null
                         };

和扩展方法

        internal static Dto.Team ToTeamDto(this Team team, string locale)
        {
            return new Dto.Team
            {
                id = team.TeamID,
                name = team.name
            };
        }

这有什么问题吗？ 我该如何修复它？

Answer 1

问题是 EF 无法将您的函数转换为 SQL。最简单的解决方案是使用 ToList 实现数据，然后使用您的函数:

var source = db.Standings
             .Where(c => c.LeagueID == leagueId)
             .ToList()
             .Select(c => new Standing
             {
                 id = c.id,
                 team = includeTeam ? c.Team.ToTeamDto("en-US") : null,
                 //other properties here
             });