feat: support THEN RETURN clauses #443
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Use THEN RETURN for returning data from INSERT/UPDATE/DELETE statements. This reduces the number of round-trips to Spanner for most use-cases. THEN RETURN clauses are not supported in BatchDml, which means that multiple DML statements that need to return values are translated to separate DML statements, instead of a BatchDmlRequest followed by N SELECT statements. Even in those cases, using THEN RETURN reduces the number of round-trips by 1. The fact that Batch DML does not support THEN RETURN is the main reason that it is recommended to use client-side generated UUIDs for primary keys when using Entity Framework. This will allow DML statements to be batched.
DML with THEN RETURN clauses are executed directly when the ExecuteDbReader method is called. This means that they can return aborted during the Execute call, which again means that these need to be in a retry loop.
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Use THEN RETURN for returning data from INSERT/UPDATE/DELETE statements. This reduces the number of round-trips to Spanner for most use-cases. THEN RETURN clauses are not supported in BatchDml, which means that multiple DML statements that need to return values are translated to separate DML statements, instead of a BatchDmlRequest followed by N SELECT statements. Even in those cases, using THEN RETURN reduces the number of round-trips by 1.
The fact that Batch DML does not support THEN RETURN is the main reason that it is recommended to use client-side generated UUIDs for primary keys when using Entity Framework. This will allow DML statements to be batched.