Question

我们决定在最近的项目中使用Linq To SQL作为我们的数据层。我们有一个功能性的解决方案，到目前为止已经处理了我们所提出的所有问题，还有一个主要问题。我们必须反复编写相同的方法来从数据库中检索稍微不同的结果集。

举个例子：

        public List<TeamBE> GetTeamsBySolutionID(Guid SolutionID)
        {
            List<TeamBE> teams = new List<TeamBE>();

            Esadmin db = new Esadmin(_connectionString);

            var qry = (from teamsTable in db.Teams
                       join solutionsTable in db.Solutions on teamsTable.SolutionID equals solutionsTable.SolutionID
                       where teamsTable.SolutionID == SolutionID
                       select new { teamsTable, solutionsTable.SolutionName });

            foreach (var result in qry)
            {
                TeamBE team = new TeamBE();

                team.TeamID = result.teamsTable.TeamID;
                team.Description = result.teamsTable.Description;
                team.Status = result.teamsTable.Status;
                team.LastModified = result.teamsTable.LastModified;
                team.SolutionID = result.teamsTable.SolutionID;
                team.SolutionName = result.SolutionName;
                team.Name = result.teamsTable.Name;
                team.LocationLevel = result.teamsTable.LocationLevel;
                team.AORDriven = result.teamsTable.AoRDriven;
                team.CriteriaID = result.teamsTable.CriteriaID ?? Guid.Empty;

                teams.Add(team);
            }
            return teams;
        }

        public TeamBE GetTeamByID(Guid TeamID)
        {
            Esadmin db = new Esadmin(_connectionString);
            TeamBE team = new TeamBE();

            var qry = (from teamsTable in db.Teams
                       join solutionsTable in db.Solutions on teamsTable.SolutionID equals solutionsTable.SolutionID
                       where teamsTable.TeamID == TeamID
                       select new { teamsTable, solutionsTable.SolutionName }).Single();

            team.TeamID = qry.teamsTable.TeamID;
            team.Description = qry.teamsTable.Description;
            team.Status = qry.teamsTable.Status;
            team.LastModified = qry.teamsTable.LastModified;
            team.SolutionID = qry.teamsTable.SolutionID;
            team.SolutionName = qry.SolutionName;
            team.Name = qry.teamsTable.Name;
            team.LocationLevel = qry.teamsTable.LocationLevel;
            team.AORDriven = qry.teamsTable.AoRDriven;
            team.CriteriaID = qry.teamsTable.CriteriaID ?? Guid.Empty;

            return team;
        }

并且持续恶作剧。

有没有办法将Linq结果作为参数传递给函数，所以我可以将对象映射放在一个函数中，而不是重复自己这么多？

Answer 1

我快速刺了一下。可能不会编译（特别是“来自团队中的teamsTalbe”），但想法是你可以分解出返回IQueryable＆lt;＆gt;的东西。虽然IQueryable返回匿名类型，但这不起作用。所以你可能需要创建一个显式类型来代替'select new {teamsTable，solutionsTable.SolutionName}'

    public List<TeamBE> GetTeamsBySolutionID(int solutionID)
    {
        Esadmin db = new Esadmin(_connectionString);
        return GetTeamsBy(db, _GetTeamsBySolutionID(db, solutionID));
    }

    IQueryable<Team> _GetTeamsBySolutionID(Esadmin db, int solutionID)
    {
        return from teamsTable in db.Teams
               where teamsTable.SolutionID == SolutionID
               select teamsTable;
    }

    List<TeamBE> GetTeamsBy(Esadmin db, IQueryable<Team> teams)
    {
        List<TeamBE> teams = new List<TeamBE>();

        var qry = (from teamsTable in teams
                   join solutionsTable in db.Solutions on teamsTable.SolutionID equals solutionsTable.SolutionID
                   select new { teamsTable, solutionsTable.SolutionName });

        foreach (var result in qry)
        {
            TeamBE team = new TeamBE();

            team.TeamID = result.teamsTable.TeamID;
            team.Description = result.teamsTable.Description;
            team.Status = result.teamsTable.Status;
            team.LastModified = result.teamsTable.LastModified;
            team.SolutionID = result.teamsTable.SolutionID;
            team.SolutionName = result.SolutionName;
            team.Name = result.teamsTable.Name;
            team.LocationLevel = result.teamsTable.LocationLevel;
            team.AORDriven = result.teamsTable.AoRDriven;
            team.CriteriaID = result.teamsTable.CriteriaID ?? Guid.Empty;

            teams.Add(team);
        }
        return teams;
    }

Answer 2

我认为您可以将qry变量声明为IEnumerable<YourDataTypeEntity>并将其传递给方法。我倾向于把它当作构造函数来做：

class MyDataType
{
  public MyDataType() {}
  public MyDataType(MyDataTypeEntity mdte)
  {
    // set properties and fields here
  }

  // ...
}

Answer 3

你可以传递一个IQueryable然后当你想要处理结果然后你迭代结果。我不确定这是你要问的那种事情，还是我对你的问题不感兴趣。

Answer 4

另请参阅AutoMapper，这是一种API，它使用基于约定的匹配算法来匹配对象中的源值与目标值。使用它可能会删除你的大部分a = b.c代码。

Answer 5

我用entityFramework实现了这样的东西：

//This returns an IQueryable of your Linq2Sql entities, here you put your query.
protected IQueryable<Team> GetTeamByIdQuery(Guid teamID)
{
    var qry = (from TeamsTable in db.Teams
               where blablabla.....
               select Teams;

    return qry;
}


//This will return your real entity
public IList<TeamBE> GetTeamById(Guid teamID)
{
    var query = this.GetTeamByIdQuery(teamID);
    IList<TeamBE> teams = ExecuteTeamQuery(query).toList<TeamBE>();

    return teams;
}


//this method will do the mapping from your L2S entities to your model entities
protected IQueryable<TeamBE> ExcuteTeamQuery(IQueryable<Team> query)
{
    return 
        query.select<Team, TeamBE> (team => 
           new TeamBE
           {
              TeamID = team.TeamID,
              Description = team.Description 
           }

}

还没有测试这么多，但它确实有效。我还在研究如何根据bitflag参数定义要加载的属性。我还没有工作但是会像：

public IQueryable<TeamBE> ExcuteTeamQuery(IQueryable<Team> query, int loadLevel)
{
    return 
        query.select<Team, TeamBE> (team => 
           new TeamBE
           {
              TeamID = team.TeamID,
              TeamMembers = (HaveToLoad(LoadLevel.TeamMembers, loadLevel)) ? team.TeamMembers : null 
           }

}


enter code here

Answer 6

尝试扩展方法：如果你有

public IQueryable<Team> GetTeams() { return db.Teams; }

尝试写作：

public IQueryable<Team> WithDivisionId(this IQueryable<Team> qry, int divisionId)
{ return (from t in qry where t.DivisionId = divisionId select t);}

通过这种方式，您可以编写多个扩展方法，可以查询任何IQueryable<Team>并将它们分层......

要获得第1分区的队伍获得9分或更多胜利以及连胜5分或以上，您可以写下：

GetTeams().WithDivisionId(1).HavingWonAtLeast(9).WithWinningStreak(5);

使Linq成为SQL DRY

6 个答案: