ALTER TABLE ... ALTER CONSTRAINT for FKs

Allow constraint attributes to be altered,
so the default setting of NOT DEFERRABLE
can be altered to DEFERRABLE and back.

Review by Abhijit Menon-Sen

diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index 7ee0aa8ca0756675415a2a3b196188b776f276fc..2609d4a8eaf340fa2b725014ac383de3deaa36f8 100644 (file)
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -46,6 +46,7 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column_name</replaceable> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
     ADD <replaceable class="PARAMETER">table_constraint</replaceable> [ NOT VALID ]
     ADD <replaceable class="PARAMETER">table_constraint_using_index</replaceable>
+    ALTER CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
     VALIDATE CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable>
     DROP CONSTRAINT [ IF EXISTS ]  <replaceable class="PARAMETER">constraint_name</replaceable> [ RESTRICT | CASCADE ]
     DISABLE TRIGGER [ <replaceable class="PARAMETER">trigger_name</replaceable> | ALL | USER ]
@@ -316,6 +317,16 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>ALTER CONSTRAINT</literal></term>
+    <listitem>
+     <para>
+      This form alters the attributes of a constraint that was previously
+      created. Currently only foreign key constraints may be altered.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>VALIDATE CONSTRAINT</literal></term>
     <listitem>

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 50341f6ef9ade55945b5234a1dd7038eb3ff36d9..ea1c309add82916e6f07e4f4437a3e07ba49a641 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -276,6 +276,8 @@ static void AlterIndexNamespaces(Relation classRel, Relation rel,
 static void AlterSeqNamespaces(Relation classRel, Relation rel,
                                   Oid oldNspOid, Oid newNspOid, ObjectAddresses *objsMoved,
                                   LOCKMODE lockmode);
+static void ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
+                                                bool recurse, bool recursing, LOCKMODE lockmode);
 static void ATExecValidateConstraint(Relation rel, char *constrName,
                                                 bool recurse, bool recursing, LOCKMODE lockmode);
 static int transformColumnNameList(Oid relId, List *colList,
@@ -2887,6 +2889,7 @@ AlterTableGetLockLevel(List *cmds)
                        case AT_SetOptions:
                        case AT_ResetOptions:
                        case AT_SetStorage:
+                       case AT_AlterConstraint:
                        case AT_ValidateConstraint:
                                cmd_lockmode = ShareUpdateExclusiveLock;
                                break;
@@ -3125,6 +3128,10 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
                        ATPrepAddInherit(rel);
                        pass = AT_PASS_MISC;
                        break;
+               case AT_AlterConstraint:                /* ALTER CONSTRAINT */
+                       ATSimplePermissions(rel, ATT_TABLE);
+                       pass = AT_PASS_MISC;
+                       break;
                case AT_ValidateConstraint:             /* VALIDATE CONSTRAINT */
                        ATSimplePermissions(rel, ATT_TABLE);
                        /* Recursion occurs during execution phase */
@@ -3304,6 +3311,9 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
                case AT_AddIndexConstraint:             /* ADD CONSTRAINT USING INDEX */
                        ATExecAddIndexConstraint(tab, rel, (IndexStmt *) cmd->def, lockmode);
                        break;
+               case AT_AlterConstraint:                /* ALTER CONSTRAINT */
+                       ATExecAlterConstraint(rel, cmd, false, false, lockmode);
+                       break;
                case AT_ValidateConstraint:             /* VALIDATE CONSTRAINT */
                        ATExecValidateConstraint(rel, cmd->name, false, false, lockmode);
                        break;
@@ -6175,6 +6185,135 @@ ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
        heap_close(pkrel, NoLock);
 }
 
+/*
+ * ALTER TABLE ALTER CONSTRAINT
+ *
+ * Update the attributes of a constraint.
+ *
+ * Currently only works for Foreign Key constraints.
+ * Foreign keys do not inherit, so we purposely ignore the
+ * recursion bit here, but we keep the API the same for when
+ * other constraint types are supported.
+ */
+static void
+ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
+                                                bool recurse, bool recursing, LOCKMODE lockmode)
+{
+       Relation        conrel;
+       SysScanDesc scan;
+       ScanKeyData key;
+       HeapTuple       contuple;
+       Form_pg_constraint currcon = NULL;
+       Constraint      *cmdcon = NULL;
+       bool            found = false;
+
+       Assert(IsA(cmd->def, Constraint));
+       cmdcon = (Constraint *) cmd->def;
+
+       conrel = heap_open(ConstraintRelationId, RowExclusiveLock);
+
+       /*
+        * Find and check the target constraint
+        */
+       ScanKeyInit(&key,
+                               Anum_pg_constraint_conrelid,
+                               BTEqualStrategyNumber, F_OIDEQ,
+                               ObjectIdGetDatum(RelationGetRelid(rel)));
+       scan = systable_beginscan(conrel, ConstraintRelidIndexId,
+                                                         true, SnapshotNow, 1, &key);
+
+       while (HeapTupleIsValid(contuple = systable_getnext(scan)))
+       {
+               currcon = (Form_pg_constraint) GETSTRUCT(contuple);
+               if (strcmp(NameStr(currcon->conname), cmdcon->conname) == 0)
+               {
+                       found = true;
+                       break;
+               }
+       }
+
+       if (!found)
+               ereport(ERROR,
+                               (errcode(ERRCODE_UNDEFINED_OBJECT),
+                                errmsg("constraint \"%s\" of relation \"%s\" does not exist",
+                                               cmdcon->conname, RelationGetRelationName(rel))));
+
+       if (currcon->contype != CONSTRAINT_FOREIGN)
+               ereport(ERROR,
+                               (errcode(ERRCODE_WRONG_OBJECT_TYPE),
+                                errmsg("constraint \"%s\" of relation \"%s\" is not a foreign key constraint",
+                                               cmdcon->conname, RelationGetRelationName(rel))));
+
+       if (currcon->condeferrable != cmdcon->deferrable ||
+               currcon->condeferred != cmdcon->initdeferred)
+       {
+               HeapTuple       copyTuple;
+               HeapTuple       tgtuple;
+               Form_pg_constraint copy_con;
+               Form_pg_trigger copy_tg;
+               ScanKeyData tgkey;
+               SysScanDesc tgscan;
+               Relation        tgrel;
+
+               /*
+                * Now update the catalog, while we have the door open.
+                */
+               copyTuple = heap_copytuple(contuple);
+               copy_con = (Form_pg_constraint) GETSTRUCT(copyTuple);
+               copy_con->condeferrable = cmdcon->deferrable;
+               copy_con->condeferred = cmdcon->initdeferred;
+               simple_heap_update(conrel, &copyTuple->t_self, copyTuple);
+               CatalogUpdateIndexes(conrel, copyTuple);
+
+               InvokeObjectPostAlterHook(ConstraintRelationId,
+                                                                 HeapTupleGetOid(contuple), 0);
+
+               heap_freetuple(copyTuple);
+
+               /*
+                * Now we need to update the multiple entries in pg_trigger
+                * that implement the constraint.
+                */
+               tgrel = heap_open(TriggerRelationId, RowExclusiveLock);
+
+               ScanKeyInit(&tgkey,
+                                       Anum_pg_trigger_tgconstraint,
+                                       BTEqualStrategyNumber, F_OIDEQ,
+                                       ObjectIdGetDatum(HeapTupleGetOid(contuple)));
+
+               tgscan = systable_beginscan(tgrel, TriggerConstraintIndexId, true,
+                                                                       SnapshotNow, 1, &tgkey);
+
+               while (HeapTupleIsValid(tgtuple = systable_getnext(tgscan)))
+               {
+                       copyTuple = heap_copytuple(tgtuple);
+                       copy_tg = (Form_pg_trigger) GETSTRUCT(copyTuple);
+                       copy_tg->tgdeferrable = cmdcon->deferrable;
+                       copy_tg->tginitdeferred = cmdcon->initdeferred;
+                       simple_heap_update(tgrel, &copyTuple->t_self, copyTuple);
+                       CatalogUpdateIndexes(tgrel, copyTuple);
+
+                       InvokeObjectPostAlterHook(TriggerRelationId,
+                                                                               HeapTupleGetOid(tgtuple), 0);
+
+                       heap_freetuple(copyTuple);
+               }
+
+               systable_endscan(tgscan);
+
+               heap_close(tgrel, RowExclusiveLock);
+
+               /*
+                * Invalidate relcache so that others see the new attributes.
+                */
+               CacheInvalidateRelcache(rel);
+       }
+
+       systable_endscan(scan);
+
+       heap_close(conrel, RowExclusiveLock);
+}
+
 /*
  * ALTER TABLE VALIDATE CONSTRAINT
  *

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index c41f1b512f6b3a1da605bcfce37583c98aad6512..0fc5b13d015bd6b80293914213e6e2f4cf2af68e 100644 (file)
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -1943,6 +1943,21 @@ alter_table_cmd:
                                        n->def = $2;
                                        $$ = (Node *)n;
                                }
+                       /* ALTER TABLE <name> ALTER CONSTRAINT ... */
+                       | ALTER CONSTRAINT name ConstraintAttributeSpec
+                               {
+                                       AlterTableCmd *n = makeNode(AlterTableCmd);
+                                       Constraint *c = makeNode(Constraint);
+                                       n->subtype = AT_AlterConstraint;
+                                       n->def = (Node *) c;
+                                       c->contype = CONSTR_FOREIGN; /* others not supported, yet */
+                                       c->conname = $3;
+                                       processCASbits($4, @4, "ALTER CONSTRAINT statement",
+                                                                       &c->deferrable,
+                                                                       &c->initdeferred,
+                                                                       NULL, NULL, yyscanner);
+                                       $$ = (Node *)n;
+                               }
                        /* ALTER TABLE <name> VALIDATE CONSTRAINT ... */
                        | VALIDATE CONSTRAINT name
                                {

diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 6723647e2e397126e6e2ba480068fd40748f1e59..9453e1dfdfa61215a6f205c874210e490bbc33b9 100644 (file)
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1209,6 +1209,7 @@ typedef enum AlterTableType
        AT_AddConstraint,                       /* add constraint */
        AT_AddConstraintRecurse,        /* internal to commands/tablecmds.c */
        AT_ReAddConstraint,                     /* internal to commands/tablecmds.c */
+       AT_AlterConstraint,                     /* alter constraint */
        AT_ValidateConstraint,          /* validate constraint */
        AT_ValidateConstraintRecurse,           /* internal to commands/tablecmds.c */
        AT_ProcessedConstraint,         /* pre-processed add constraint (local in

diff --git a/src/test/regress/expected/foreign_key.out b/src/test/regress/expected/foreign_key.out
index 04668a8886cec869cab4466ab51083a5f0276e6e..0299bfe873070b81eb5dd36fd24a37893d09d0d7 100644 (file)
--- a/src/test/regress/expected/foreign_key.out
+++ b/src/test/regress/expected/foreign_key.out
@@ -1132,6 +1132,15 @@ CREATE TEMP TABLE fktable (
     id int primary key,
     fk int references pktable deferrable initially deferred
 );
+-- check ALTER CONSTRAINT
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE;
+-- illegal option
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE INITIALLY DEFERRED;
+ERROR:  constraint declared INITIALLY DEFERRED must be DEFERRABLE
+LINE 1: ...e ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE INITIALLY ...
+                                                             ^
+-- reset
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY DEFERRED;
 INSERT INTO pktable VALUES (5, 10);
 BEGIN;
 -- doesn't match PK, but no error yet
@@ -1142,6 +1151,16 @@ UPDATE fktable SET id = id + 1;
 COMMIT;
 ERROR:  insert or update on table "fktable" violates foreign key constraint "fktable_fk_fkey"
 DETAIL:  Key (fk)=(20) is not present in table "pktable".
+-- change the constraint definition and retest
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY IMMEDIATE;
+BEGIN;
+-- doesn't match PK, should throw error now
+INSERT INTO fktable VALUES (0, 20);
+ERROR:  insert or update on table "fktable" violates foreign key constraint "fktable_fk_fkey"
+DETAIL:  Key (fk)=(20) is not present in table "pktable".
+COMMIT;
+-- reset
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY DEFERRED;
 -- check same case when insert is in a different subtransaction than update
 BEGIN;
 -- doesn't match PK, but no error yet

diff --git a/src/test/regress/sql/foreign_key.sql b/src/test/regress/sql/foreign_key.sql
index 377b36c226b5baa394ca69290f463696ab5e4207..531c881f6318255b272ff1008ed65de356b7f952 100644 (file)
--- a/src/test/regress/sql/foreign_key.sql
+++ b/src/test/regress/sql/foreign_key.sql
@@ -818,6 +818,13 @@ CREATE TEMP TABLE fktable (
     fk int references pktable deferrable initially deferred
 );
 
+-- check ALTER CONSTRAINT
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE;
+-- illegal option
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE INITIALLY DEFERRED;
+-- reset
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY DEFERRED;
+
 INSERT INTO pktable VALUES (5, 10);
 
 BEGIN;
@@ -831,6 +838,19 @@ UPDATE fktable SET id = id + 1;
 -- should catch error from initial INSERT
 COMMIT;
 
+-- change the constraint definition and retest
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY IMMEDIATE;
+
+BEGIN;
+
+-- doesn't match PK, should throw error now
+INSERT INTO fktable VALUES (0, 20);
+
+COMMIT;
+
+-- reset
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY DEFERRED;
+
 -- check same case when insert is in a different subtransaction than update
 
 BEGIN;