如何在linq查询中调用自定义方法

Question

i write a custom method like below :

 DateTime GetGregorianDate(string date)
    {
       return  new DateTime(int.Parse(date.Substring(0, 4)), int.Parse(date.Substring(5,    2)), int.Parse(date.Substring(8, 2)), new System.Globalization.PersianCalendar());
    }

and i want call this method in linq query like below :

 dynamic GetPlayerListByTeamName(string teamCode, FutsalEntities myEntity)
    {
        var player = (from p in myEntity.Players
                     where p.TeamCode == teamCode && (GetGregorianDate(p.ContractDateTo) <= DateTime.Now) ? true : false
                     select new { p.MeliCode, p.BearthDate, p.ContractNumber, p.InsuranceNumber, p.ContractDate, p.Mobile });
        return player;

    }

This is where the code is called :

  private void cmbTeams_SelectedIndexChanged(object sender, EventArgs e)
    {
        using (FutsalEntities myEntity = new FutsalEntities())
        {
            if (cmbTeams.SelectedIndex != -1 && myEntity.Players.Count() != 0)
            {
               dgPlayerList.DataSource =  GetPlayerListByTeamName(cmbTeams.SelectedValue.ToString(), myEntity);

but when i run application get this error :

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

Is there any way to call this method in linq query?

Answer 1

Linq to Entities can't translate your method into SQL and execute it on server side. The only way to call your custom method is to move query into memory - eg by calling AsEnumerable() or ToList()

var players = from p in myEntity.Players.AsEnumerable()                      
              where GetGregorianDate(p.ContractDateTo) <= DateTime.Now
              select new { 
                  p.Name,
                  p.BearthDate, 
                  p.ContractNumber, 
                  p.InsuranceNumber, 
                  p.ContractDate, 
                  p.Mobile 
              };

Keep in mind, that this will transfer all players data over the network to local computer.

Answer 2

将DateTime.Now转换为波斯日期，将其存储在变量中，然后在查询中使用该变量，以便服务器端查询将进行波斯日期比较。