Support stored procedures without a table mapping

[roji]

Stored procedure mapping (#28553) currently requires that a table mapping be defined; the table mapping is necessary in order for us to properly perform topological sort (e.g. know about dependencies between tables). It makes sense for users to use views/functions for querying and only sprocs for updating, in which case a table mapping isn't strictly speaking necessary.

See conversation in #28553 (comment)

[PolkageistHS]

In the meantime, can the exception message be updated to reflect that non-tables are not supported? It still says "An entity type that isn't mapped to a table must be mapped to insert, update and delete stored procedures." but the code doesn't allow any SP mapping to non-tables.

efcore/src/EFCore.Relational/Infrastructure/RelationalModelValidator.cs

Line 249 in afe9bc1

throw new InvalidOperationException(RelationalStrings.StoredProcedureUnmapped(entityType.DisplayName()));

efcore/src/EFCore.Relational/Properties/RelationalStrings.resx

Lines 1094 to 1096 in afe9bc1

	<data name="StoredProcedureUnmapped" xml:space="preserve">
	<value>The entity type '{entityType}' was configured to use some stored procedures and is not mapped to any table. An entity type that isn't mapped to a table must be mapped to insert, update and delete stored procedures.</value>
	</data>