如何存储Linq查询并在以后使用？

Question

I'm doing a wpf App and i've got a bit of an issue i would like to ask you about.

I'm querying a database on the window level and i pass the result of the query to a method in my object like this :

Window level code :

payrollEmailManager.SetListOfSalariesToEmailTo(
    from Record in SqlInfo.SqlTable.T_SALs 
    where Record.EtatPaie == 3 
    select new {
        Matricule = Record.MatriculeSalarie, 
        Nom = Record.Nom,
        Prenom = Record.Prenom, 
        Email = Record.EMail });

This is my Method Definition :

public void SetListOfSalariesToEmailTo(object _ListOfSalaryToRecieveMail)
{
   ListOfSalary = _ListOfSalaryToRecieveMail;
}

Where ListOfSalary is also of type object .

Now here is the issue for me, I have another method where I want to go trough each record of listofsalary and get the information I selected in query like Matricule or Email , something like this :

public void SendEmail()
{
    foreach(var Salary in (dynamic)ListOfSalary)
    {
        Mail.To.Add(Salary.????
    }
}

I can't reference the Nom column or the Email column any advice ??

Answer 1

If you consider your following query:

var query = from Record in SqlInfo.SqlTable.T_SALs 
            where Record.EtatPaie == 3 
            select new { 
                Matricule = Record.MatriculeSalarie, 
                Nom = Record.Nom, 
                Prenom = Record.Prenom, 
                Email = Record.EMail 
            };

After running this line the query is not yet executed to database. Only when you materialize it (using functions like ToList() / ToArray() / FirstOrDefault etc.) it is actually being executed in the database and information is returned.

Therefore if you just do SomeFunction(query); it does not execute the query and you can store it for later execution.

However you do need to change your code a bit:

• The function should not get object but IQueryable<T>

   public void SetListOfSalariesToEmailTo(IQueryable<T> query) 

• As you want to store the query you need to later on know the type of each item. To do so do not use an anonymous object ( new { } ) in the select. Use instead a custom object or use c# 7.0 named tuples and then the function will look like:

   var query = from Record in SqlInfo.SqlTable.T_SALs where Record.EtatPaie == 3 select new SomeType { Matricule = Record.MatriculeSalarie, Nom = Record.Nom, Prenom = Record.Prenom, Email = Record.EMail }; public void SetListOfSalariesToEmailTo(IQueryable<SomeType> query) { ListOfSalary = query; } 

---

You can still use object and dynamic as you did, and just access the properties, but you will not have the intellisense showing you the properties and options, as it does not know the concrete type.