How to: Supply Initial Data for the Entity Framework Core Data Model

• Nov 11, 2022
• 3 minutes to read

After you have introduced a data model, you may need to have the application populate the database with a predefined set of objects. In this topic, you will learn how to add data to the database in code when the application runs. For this purpose, the code that creates an Employee object with the associated Task is demonstrated here.

In this example, it is assumed that you have created an XAF solution with an Entity Framework Core data model in accordance with the following help topic: Use the Entity Framework Core Data Model.

Implement the Module Updater

Open the MySolution.Module\DatabaseUpdate\Updater.cs and override the ModuleUpdater.UpdateDatabaseAfterUpdateSchema method as shown below.

C#

public class Updater : ModuleUpdater {
    public Updater(IObjectSpace objectSpace, Version currentDBVersion) : base(objectSpace, currentDBVersion) { }
    public override void UpdateDatabaseAfterUpdateSchema() {
        if (ObjectSpace.GetObjects<Employee>().Count == 0) {
            var employee = ObjectSpace.CreateObject<Employee>();
            employee.FirstName = "Mary";
            employee.LastName = "Tellitson";
            var task = ObjectSpace.CreateObject<Task>();
            task.Subject = "Check reports";
            task.AssignedTo = employee;
        }
        ObjectSpace.CommitChanges();
    }
}

public class Employee : BaseObject {
    public virtual string FirstName { get; set; }
    public virtual string LastName { get; set; }
    publuc virtual IList<Task> Tasks { get; set; } = new ObservableCollection<Task>();
    // ...
}

public class Task : BaseObject {
    publuc virtual string Subject { get; set; }
    public virtual Employee AssignedTo { get; set; }
    // ...
}

// Make sure that you use options.UseChangeTrackingProxies() in your DbContext settings.

In the code above, an Employee object with an associated Task is created if there are no Employee records in the database. As you can see, XAF uses an Object Space object to manipulate persistent objects (see Create, Read, Update and Delete Data).

Note

To learn more about updating the application database, refer to the Create and Update the Application’s Database topic.

Add the ModuleInfo Entity

The ModuleInfo entity mapped to the ModuleInfo table is used when the XafApplication.CheckCompatibilityType property is set to ModuleInfo, to store the version information of the application modules. When a module assembly version is incremented, XAF compares the actual module versions with versions stored in the database. If versions differ, the database must be updated. To support the database update, an entity that implements the data model must have the IModuleInfo interface.

Note

If you use the Solution Wizard to create an XAF solution, the ModuleInfo entity is added automatically by default.

XAF provides a built-in IModuleInfo implementor: the ModuleInfo entity. Register this entity within your DbContext descendant.

C#

public class MySolutionEFCoreDbContext : DbContext {
    // ...
    public DbSet<DevExpress.ExpressApp.EFCore.Updating.ModuleInfo> ModuleInfo { get; set; }
}

After applying the changes above, the Employee and Task records will be created in the application database.