Question

Ladislav, sorry maybe i’m not correctly posed question. Suppose in WinForm application i’m creating new object:

        var newEmission = _emissionBindingSource.Current as Emission;
        if (newEmission == null) return;
        newEmission.SharesNumber = _context.GetNewSharesNumber();

    public int GetNewSharesNumber()
    {
        return Shares.Max(s => s.Number)+1;
    }`

but Max s.Number is not changing untill i havn’t saved previous inserted object. So, in this case i must save every object separatly?

UPDATE 1
Suppose i have created new object emission. I took Shares.Max(s => s.Number)+1 to SharesNumber field of new object. Now i want create second emission object, and SharesNumber of this object must be greater to 1 then previous object. I can achieve this only if i save firstly created object.

Answer 1

    var newEmission = _emissionBindingSource.Current as Emission;
    if (newEmission == null) return;
    newEmission.SharesNumber = _context.GetNewSharesNumber();

public int GetNewSharesNumber()
{
    // this will always query DB for max value
    return Shares.CreateSourceQuery().Max(s => s.Number)+1;
}

But I believe you should use some sort of stored procedure to assign new number or use auto increment column because if you have multiple users using multiple applications, there may be the case of duplicate numbers.