Windows Phone SQL Server CE - Retrieve underlying database schema for upgrade - linq

Question

Windows Phone 7.1 supports SQL Server CE and LINQ to SQL, as well as upgrading the database via DatabaseSchemaUpdater.
On other platforms I would read the database schema tables (e.g. sys.objects) to view the current schema and work out what tables/columns need to be upgraded.
Given that no direct SQL access is allowed on Windows Phone, how can retrieve the current database schema?

Answer 1

SQL Server CE still includes the INFORMATION_SCHEMA.TABLES and INFORMATION_SCHEMA.COLUMNS tables, but it is a little tricky to access them as no direct SQL access is allowed.
However, you can create a DataContext which maps to these tables:
public class SchemaContext : DataContext
{
public SchemaContext()
: base("Data Source=isostore:/Database.sdf")
{
if (!this.DatabaseExists())
{
throw new InvalidOperationException("Cannot use the SchemaContext on a database which doesn't exist");
}
}
public Table<Table> Tables;
public Table<Column> Columns;
[Table(Name = "INFORMATION_SCHEMA.Columns")]
public class Column
{
[Column(Name = "TABLE_NAME")]
public string TableName { get; set; }
[Column(Name = "COLUMN_NAME")]
public string Name { get; set; }
[Column(Name = "DATA_TYPE")]
public string DataType { get; set; }
[Column(Name = "ORDINAL_POSITION")]
public int OrdinalPosition { get; set; }
[Column(Name = "IS_NULLABLE")]
public string IsNullableString { get; set; }
public bool IsNullable
{
get { return this.IsNullableString == "YES"; }
set { this.IsNullableString = value ? "YES" : "NO"; }
}
}
[Table(Name = "INFORMATION_SCHEMA.Tables")]
public class Table
{
[Column(Name = "TABLE_NAME")]
public string Name { get; set; }
[Column(Name = "TABLE_TYPE")]
public string Type { get; set; }
}
}
You can then read the schema with the following code:
using (var schemaContext = new SchemaContext())
{
foreach (var table in schemaContext.Tables)
{
}
}
It's important to create a separate context for these tables, as otherwise the DataContext.CreateDatabase call will attempt to create these schema tables, which will fail.

Answer 2

There is a Walkthrough for Updating a Local Database Application for Windows Phone on MSDN which advocates using the DatabaseSchemaVersion on the DatabaseSchemaUpdater - i.e:
// Set the new database version.
DatabaseSchemaUpdater dbUpdater = db.CreateDatabaseSchemaUpdater();
dbUpdater.DatabaseSchemaVersion = APP_VERSION;
dbUpdater.Execute();
You can query the version and add the bits that you add in each release, without having to worry about the current schema (after all, it'll be a known configuration as long as you remember to keep the version numbers updated correctly.)