feat: add NewTxnContext for validated multi-mutation transactions#7
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Insert/Upsert/Update each open a dgman transaction with SetCommitNow and commit per call, so a caller cannot group several typed mutations into one atomic commit; consumers that need multi-mutation atomicity drop to raw dgman and lose validation. Add TxnContext and client.NewTxnContext, which open one dgman transaction without SetCommitNow and stage any number of mutations and deletes until Commit. Each staged Insert/Upsert/Update runs the same pre-mutation pipeline as the single-shot methods (default population, struct validation) and the same unique-constraint error translation, so grouping mutations costs no validation. DeletePredicate emits the n-quad `<uid> <predicate> * .` to clear a scalar predicate or all edges of a predicate. The transaction holds a pooled connection for its lifetime and returns it on Commit or Discard; a deferred Discard after Commit is a safe no-op.
Add embedded-engine (file://) and remote (dgraph://) table-driven tests for NewTxnContext: - validation fires inside the transaction and blocks commit - multi-op DeleteEdge + DeleteNode + Upsert commit together; an error before Commit leaves the store unchanged - a duplicate unique insert returns a typed *UniqueError - DeletePredicate clears a scalar predicate while the node survives The dgraph:// cases activate when DGDAO_TEST_ADDR is set. The embedded engine commits each successful mutation immediately, so the atomicity sibling triggers a pre-commit error (rejected before any write is applied) to assert "store unchanged"; true rollback of already-staged valid writes is exercised by the dgraph:// job.
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What
Adds
Client.NewTxnContext— a validated, deferred-commit read-write transaction — so callers can run several mutations in one atomically-committed transaction:Upsert(obj, predicates...),Update(obj),Insert(obj)DeleteEdge(uid, predicate, targetUIDs...),DeleteNode(uids...),DeletePredicate(uid, predicate)Commit(),Discard()Why
The typed write methods (
Insert/Upsert/Update) each open a dgman transaction withSetCommitNow(), so they auto-commit per call. A caller that needs to group several mutations into one atomic commit (for example: delete an owner's old edges and nodes, then upsert the owner) cannot express that through the typed API without dropping to raw dgman — which bypasses the client's validation, defaulting, and unique-error translation.NewTxnContextcloses that gap.Behavior
Each staged write runs the same defaulting, validation, and unique-constraint error translation (to
*UniqueError) as its single-shot counterpart — it reusesvalidateStruct,applyDefaults, andparseUniqueError. Nothing reaches the database untilCommit()succeeds;Discard()abandons every staged mutation.Note: unlike the single-shot writes, the transaction path does not run autoSchema schema creation, so a type written only via
NewTxnContextmust already have its schema applied (documented in theTxnContextgodoc).Tests
txn_test.gocovers validation-fires-in-txn, multi-op atomicity, unique-error translation, andDeletePredicate. Unit suite green (plain and-race); the real-Dgraph CI job exercises true deferred-commit rollback that the embedded file engine cannot.Docs
README gains a section on
NewTxnContextnext to the atomic-operations docs; CHANGELOG updated for v0.7.0.