Caller identity

It is often desirable to pass some notion of client-side identity along with each query sent to the database, so that some useful database-side logic could capture this identity (in addition to executing the query itself).

One example is database-side logging/auditing of all queries, and linking each query (and/or modifications made by it) to a specific caller identity (ex. "User Id") which triggered that query. Such caller identity would become part of the context of that query.

TinyORM leverages CONTEXT_INFO feature of SQL Server to automatically send 16 bytes of client-side caller identity (ex. a Guid) with each query.

On the client side you can use the .CallerIdentityDelegate property of DbContext instance to set a custom caller identity delegate.

On the database side a query (or a trigger) can read the caller identity from first 16 bytes of CONTEXT_INFO():

SELECT CAST(CONTEXT_INFO() AS UNIQUEIDENTIFIER);

Full example:

var dbContext = DbContext.Create("connection string");

dbContext.CallerIdentityDelegate = () =>
{
	// replace with your context-specific user id retrieval logic 
	Guid user_id = new Guid("12345678-ABCD-ABCD-ABCD-0123456789AB");
	return new CallerIdentity(user_id);
});

{
	dbContext.QueryAsync("SELECT CAST(CONTEXT_INFO() AS UNIQUEIDENTIFIER);").Dump();
	// [ key: "UserIdentity", value: 12345678-abcd-abcd-abcd-0123456789ab ]
}

If context identity is not explicitly set on a DbContext instance, Guid.Empty is used by default.