Automatic schema updates

This topic describes how to work with database schema updates, when upgrading Episerver websites. Schema updates can be done manually, or automatically as described here.

How it works

The Update-EPiDatabase cmdlet manually updates the the database scheme as described in Updating configuration and database schemas. You can configure the site to automatically apply updates to the SQL schema during site initialization. 

When the site starts, it compares the assembly version and the database version. If the database version is lower than the assembly version and automatic updates are enabled, it applies the SQL schema updates. (The SQL files are embedded resources in the assembly.) To enable automatic schema updates, add attribute updateDatabaseSchema="true" to the episerver.framework element in configuration as shown below:

<episerver.framework updateDatabaseSchema="true">

If you enable automatic schema updates, you can interact with the schema upgrade process by registering an implementation of IDatabaseSchemaValidator in the IOC container. The interface has two methods:

• IsDatabaseUpdateAllowed. The schema calls this method first where an implementation can check if an automatic update should be allowed.
• BeforeUpdating. If all validators allow automatic schema update, the schema calls the method before it performs the actual update, so you can perform some action such a backup of the database.

Note: Validators are also called if automatic schema creation as described in Installing database schemas has been enabled and a new schema is about to be deployed.

The following example shows a basic implementation that allows updates but takes a database backup:

public class BackupDatabaseValidator : IDatabaseSchemaValidator
    {
        private readonly string _backupFolder;

        public BackupDatabaseValidator(string backupFolder)
        {
            _backupFolder = backupFolder;
        }

        public bool IsDatabaseUpdateAllowed(ConnectionStringSettings connectionStringSettings)
        {
            return true;
        }

        public void BeforeUpdating(ConnectionStringSettings connectionStringSettings)
        {
            var sqlConStrBuilder = new SqlConnectionStringBuilder(connectionStringSettings.ConnectionString);

            var backupFileName = String.Format(CultureInfo.InvariantCulture, "{0}-{1}.bak", sqlConStrBuilder.InitialCatalog, DateTime.Now.ToString("yyyy-MM-dd"));
            var backupFilePath = Path.Combine(_backupFolder, backupFileName);

            using (var connection = new SqlConnection(sqlConStrBuilder.ConnectionString))
            {
                var query = String.Format("BACKUP DATABASE {0} TO DISK='{1}'",
                    sqlConStrBuilder.InitialCatalog, backupFilePath);

                using (var command = new SqlCommand(query, connection))
                {
                    connection.Open();
                    command.ExecuteNonQuery();
                }
            }
        }
    }

The following example allows only automatic updates when running on LocalDB (typical development environment):

public class LocalDBDatabaseValidator : IDatabaseSchemaValidator
    {
        public void BeforeUpdating(System.Configuration.ConnectionStringSettings connectionStringSettings)
        {}

        public bool IsDatabaseUpdateAllowed(System.Configuration.ConnectionStringSettings connectionStringSettings)
        {
            var sqlConStrBuilder = new SqlConnectionStringBuilder(connectionStringSettings.ConnectionString);
            return sqlConStrBuilder.DataSource.StartsWith("(LocalDB)", StringComparison.OrdinalIgnoreCase);
        }
    }

You can register several validators. For example, if both validators in the previous examples are registered, updates are allowed only when running on LocalDB. and it makes a backup before it applies the update.

Related topic

• Updating configuration and database schemas
• Installing database schemas

Last updated: Sep 21, 2015