Function domainAddConstraint

src/backend/commands/typecmds.c:3562–3687

* domainAddConstraint - code shared between CREATE and ALTER DOMAIN */

 * domainAddConstraint - code shared between CREATE and ALTER DOMAIN
 */
static char *
domainAddConstraint(Oid domainOid, Oid domainNamespace, Oid baseTypeOid,
					int typMod, Constraint *constr,
					const char *domainName, ObjectAddress *constrAddr)
{
	Node	   *expr;
	char	   *ccbin;
	ParseState *pstate;
	CoerceToDomainValue *domVal;
	Oid			ccoid;

	/*
	 * Assign or validate constraint name
	 */
	if (constr->conname)
	{
		if (ConstraintNameIsUsed(CONSTRAINT_DOMAIN,
								 domainOid,
								 constr->conname))
			ereport(ERROR,
					(errcode(ERRCODE_DUPLICATE_OBJECT),
					 errmsg("constraint \"%s\" for domain \"%s\" already exists",
							constr->conname, domainName)));
	}
	else
		constr->conname = ChooseConstraintName(domainName,
											   NULL,
											   "check",
											   domainNamespace,
											   NIL);

	/*
	 * Convert the A_EXPR in raw_expr into an EXPR
	 */
	pstate = make_parsestate(NULL);

	/*
	 * Set up a CoerceToDomainValue to represent the occurrence of VALUE in
	 * the expression.  Note that it will appear to have the type of the base
	 * type, not the domain.  This seems correct since within the check
	 * expression, we should not assume the input value can be considered a
	 * member of the domain.
	 */
	domVal = makeNode(CoerceToDomainValue);
	domVal->typeId = baseTypeOid;
	domVal->typeMod = typMod;
	domVal->collation = get_typcollation(baseTypeOid);
	domVal->location = -1;		/* will be set when/if used */

	pstate->p_pre_columnref_hook = replace_domain_constraint_value;
	pstate->p_ref_hook_state = (void *) domVal;

	/*
	 * GPDB: transformExpr scribbles on the input, but we need to keep it intact
	 * because we dispatch it afterwards.
	 */
	constr = (Constraint *) copyObject(constr);
	expr = transformExpr(pstate, constr->raw_expr, EXPR_KIND_DOMAIN_CHECK);