Add support for multi-tenant systems with shared DB and discriminator columns

[kbaley]

This issue was transferred from a private repository

The multi-tenant with shared DB and discriminator columns approach is probably the most used by SaaS providers when approaching a new business. In such scenario their customers are probably small businesses with low volumes of data. In such a case it might not be worth going directly to the next level (separate storage) and it's worth supporting shared DB and discriminator columns.

Support for such scenario can implemented in a non-breaking way by leveraging the ContextBag passed to ISagaPersister and IFindSagas. It's enough to augment a persister configuration with something like:

var persister  = endpointConfig.UserPerisistence<Something>();
persister.UseMultiTenantDiscriminator( discriminatorColumnName, discrimnatorValueKeyName );

and then change the internal persister implementation so that:

• if the above configuration is set
• a behavior in the pipeline sets the discriminator value in the ContextBag
• when the persister is invoked
• discriminator value is extracted from the ContextBag
• and defined column name is used to configure the query issued to underlying storage