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.