ModuleUpdater Class
A Module updater. Allows you to handle a database update when the application version changes.
Namespace: DevExpress.ExpressApp.Updating
Assembly: DevExpress.ExpressApp.v23.2.dll
NuGet Package: DevExpress.ExpressApp
Declaration
Remarks
An XAF application automatically checks application and database version compatibility on each start. The application compares module versions stored in the database with actual module versions. If versions do not match, the application collects persistent classes and automatically updates the database schema. However, you may need to convert the database data to reflect changes in your application.
When you add a new module via the New Module template, the Updater.cs (Updater.vb) file is automatically created in the module’s project. This file contains the declaration of the ModuleUpdater class’ descendant. To handle differences between versions of an application, override the following descendant’s methods:
| Method | Description |
|---|---|
| ModuleUpdater.UpdateDatabaseBeforeUpdateSchema | Override this method to specify the database update code that should be executed before the database schema is updated. |
| ModuleUpdater.UpdateDatabaseAfterUpdateSchema | Override this method to specify the database update code that should be executed after the database schema is updated. |
When you override these methods, you can use the following protected properties:
| Property | Description |
|---|---|
ObjectSpace |
This property provides access to an IObjectSpace object that can be used for database update operations. Do not use a custom Object Space to update the database. Instead, perform all the required operations via the Object Space returned by this property. |
CurrentDBVersion |
This property returns the module assembly’s version stored in the database. If the database does not exist, the version is 0.0.0.0. Use this information to determine which updates to the database are necessary. |
The following code snippet contains a sample Updater class’ implementation. Note the use of the ObjectSpace and CurrentDBVersion properties.
public class Updater : DevExpress.ExpressApp.Updating.ModuleUpdater {
public Updater(IObjectSpace objectSpace, Version currentDBVersion) :
base(objectSpace, currentDBVersion) { }
public override void UpdateDatabaseAfterUpdateSchema() {
base.UpdateDatabaseAfterUpdateSchema();
if(CurrentDBVersion < new Version("1.5.0.0")){
Position developerPosition =
ObjectSpace.FirstOrDefault<Position>(position => position.Title == "Developer");
if(developerPosition == null) {
developerPosition = ObjectSpace.CreateObject<Position>();
developerPosition.Title = "Developer";
developerPosition.Save();
}
Position managerPosition =
ObjectSpace.FirstOrDefault<Position>(position => position.Title == "Manager");
if(managerPosition == null) {
managerPosition = ObjectSpace.CreateObject<Position>();
managerPosition.Title = "Manager";
managerPosition.Save();
}
}
ObjectSpace.CommitChanges();
}
}
Methods to Acess and Modify the Database Directly
You can use the following protected methods to execute custom SQL queries:
| Method | Description |
|---|---|
int ExecuteNonQueryCommand(string commandText, bool silent) |
Executes the SQL statement specified by the first parameter. If the second parameter is false and an error occurs when the statement is executed, an exception is thrown. If the second parameter is true and an error occurs when executing the statement, the return value is -1. On success, it returns the number of rows affected. |
object ExecuteScalarCommand(string commandText, bool silent) |
Executes the SQL query specified by the first parameter. If the second parameter is false and an error occurs when the query is executed, an exception is thrown. If the second parameter is true and an error occurs when the query is executed, the return value is -1. On success, the method returns the first column of the first row in the result set that matches the query. |
IDataReader ExecuteReader(string commandText, bool silent) |
Executes the SQL command specified by the first parameter. If the second parameter is false and an error occurs when the command is executed, an exception is thrown. If the second parameter is true and an error occurs when the query is executed, the returned value is null (Nothing in VB). On success, it returns the IDataReader object. |
You can also use a number of protected methods that are wrappers for frequently used queries. The following table lists these methods. Note that currently these method implementations are specific to Microsoft SQL Server and may not work with different database engines. If you run into an exception when using these methods with non-Microsoft SQL Server databases, you can use the ExecuteNonQueryCommand, ExecuteScalarCommand, and ExecuteReader commands, and pass the corresponding query as a parameter.
| Method | Description |
|---|---|
bool TableExists(string name) |
Checks if a table exists. Returns true if the table exists; otherwise, false. |
void DropTable(string name, bool silent) |
Removes a table. If the second parameter is false and an error occurs during removal, an exception is thrown. If the second parameter is true and an error occurs during removal, an execution is not interrupted. |
void DropColumn(string tableName, string columnName) |
Removes a column from a table. |
void DropIndex(string tableName, string indexName) |
Removes an index from a table. |
void DropConstraint(string tableName, string constraintName) |
Removes a constraint from a table. |
void RenameTable(string sourceTableName, string destinationTableName) |
Renames a table. The first parameter is the old table name and the second is the new name. |
void RenameColumn(string tableName, string currentColumnName, string newColumnName) |
Renames a column. The first parameter is the table name, the second is the old column name, and the third is the new column name. |
void UpdateXPObjectType(string oldTypeName, string newTypeName, string assemblyName) |
Updates the XPObjectType table. Finds the row where the TypeName column value is the same as the first parameter. In this row, changes the TypeName column to the value of the second parameter and changes the AssemblyName column to the value of the third parameter. The UpdateXPObjectType method only updates the database. You should manually reload changed XPObjectType instances using the Session.Reload method. |
void DeleteObjectType(string typeName) |
Deletes a row from the XPObjectType table where the TypeName column value equals the passed string parameter. |
The protected methods described above log their activities in the application log file. To see use examples of these methods, refer to the following topic: Handle Renamings and Deletions of Business Classes and their Properties.
Important
These methods cannot be used when the application is connected with the database via a Middle-tier Application Server, a Data Store Pool (XpoDefault.GetConnectionPoolString), or a Cached Data Store. In these scenarios (except for the Middle-tier Application Server), another approach can be used: cast the object space to XPObjectSpace, access its XPObjectSpace.Session member, and use corresponding methods of the Session class. For more information, refer to the following topic: Direct SQL Queries.
For more information about updating the database, refer to the following topic: Update Application and Database Versions using the ModuleInfo Table.
Note
You can have multiple module updaters per module. To register extra updaters, edit the ModuleBase.GetModuleUpdaters method’s implementation located in the Module.cs (Module.vb) file. You can return ModuleUpdater.EmptyModuleUpdaters in this method’s override if your module does not require database updates. When this method is not overridden, the module updaters are automatically collected via the reflection.