fix(09): WR-19 expose the write transaction to hooks and scopes through TxFromContext

modules/cabana/tx_context.go

@@ -0,0 +1,33 @@
+package cabana
+
+import (
+	"context"
+
+	"gorm.io/gorm"
+)
+
+type txContextKey struct{}
+
+// withTx returns ctx carrying the transaction a write is running in.
+func withTx(ctx context.Context, tx *gorm.DB) context.Context {
+	if tx == nil {
+		return ctx
+	}
+	return context.WithValue(ctx, txContextKey{}, tx)
+}
+
+// TxFromContext returns the database transaction a write route is running in,
+// for the context handed to a lifecycle hook (pact.FormBeforeCreate and the
+// other Form and Relation hooks) or a scope (pact.FormExtendQuery) that runs
+// inside it. A hook that has to read the database should use this handle
+// instead of the application pool: it then sees the same snapshot as the write
+// and does not take a second connection while the transaction holds row locks.
+// The handle is valid only until the hook returns. The second result is false
+// on routes that do not run in a transaction, such as the list.
+func TxFromContext(ctx context.Context) (*gorm.DB, bool) {
+	if ctx == nil {
+		return nil, false
+	}
+	tx, ok := ctx.Value(txContextKey{}).(*gorm.DB)
+	return tx, ok && tx != nil
+}