Question

In my DALs I currently use a new DataContext instance for each method, i.e. create the context for each data call, then dispose it (with using). I remember I read that was sort of a best practice.

Now I think that I probably better use one common DataContext per DAL which will require less lines to write and will allow to update changes in the database without attaching the entities to the newly created context.

But I am not sure whether this will impact the productivity of the application. Are there negative things which may appear with this new approach, like maybe “each context reserves a connection line with a database” or “there are only a limited number of contexts available per application“?

Answer 1

From what I read and my own conclusion, the basic rule is: use a single DataContext instance for each short time set of operations, this means:

1. Use new (separate) instance of DataContext for each operation (transaction) in long living parent objects, such as DALs. For example, the main form has a DAL which uses a DataContext, the main form is the most long living object in a desktop application, thus having a single instance of a DataContext to serve all the main form data operations will not be a good solution due to the increasing cache and risk of the data to become obsolete.

2. Use single (common) instance of DataContext for all operations in short time living parent objects. For example, if we have a class which executes a set of data operations in a short amount of time, such as takes data from a database, operates with them, updates them, saves the changes to the database and gets disposed, we better create one single instance of the DataContext and use it in all the DAL methods. This relates to a web applications and services as well since they are stateless and are being executed per request.

Example of when I see a requirement of a common DataContext:

DAL:

// Common DAL DataContext field.
DataContext Context = new DataContext();

public IEnumerable<Record> GetRecords()
{
    var records = Context.Records;

    foreach (var record in records)
    {
        yield return record;
    }    
}

public void UpdateData()
{
    Context.SaveChanges();
}

BLL:

public void ManageData()
{
    foreach (var record in DAL.GetRecords())
    {
         record.IsUpdated = true;
         DAL.UpdateData();
    }
}