add option to handle nil Valuers

conn.go

@@ -17,6 +17,8 @@ import (
 	"github.com/jackc/pgx/v5/pgtype"
 )
 
+type AfterPgxConnectFunc func(ctx context.Context, pgxconn *Conn) error
+
 // ConnConfig contains all the options used to establish a connection. It must be created by ParseConfig and
 // then it can be modified. A manually initialized ConnConfig will cause ConnectConfig to panic.
 type ConnConfig struct {
@@ -41,6 +43,11 @@ type ConnConfig struct {
 	// functionality can be controlled on a per query basis by passing a QueryExecMode as the first query argument.
 	DefaultQueryExecMode QueryExecMode
 
+	// AfterPgxConnect is utilized to modify the pgx.Conn value, such as adding options to the TypeMap value.  This is
+	// called after the AfterConnect function is called, if supplied.  If this returns an error, the connection attempt
+	// fails.
+	AfterPgxConnect AfterPgxConnectFunc
+
 	createdByParseConfig bool // Used to enforce created by ParseConfig rule.
 }
 
@@ -259,6 +266,13 @@ func connect(ctx context.Context, config *ConnConfig) (c *Conn, err error) {
 		return nil, err
 	}
 
+	if config.AfterPgxConnect != nil {
+		if err := config.AfterPgxConnect(ctx, c); err != nil {
+			c.Close(ctx)
+			return nil, err
+		}
+	}
+
 	c.preparedStatements = make(map[string]*pgconn.StatementDescription)
 	c.doneChan = make(chan struct{})
 	c.closedChan = make(chan error)

pgtype/pgtype.go

@@ -212,6 +212,10 @@ type Map struct {
 	// to be built up. There are default functions placed in this slice by NewMap(). In most cases these functions
 	// should run last. i.e. Additional functions should typically be prepended not appended.
 	TryWrapScanPlanFuncs []TryWrapScanPlanFunc
+
+	// NilHandlers is a slice of functions that is utilized to handle the case where a driver.NamedValue instance is considered
+	// nil by pgx, but may need to be subsituted for a different value.
+	NilHandlers []NilHandler
 }
 
 func NewMap() *Map {
@@ -1037,6 +1041,17 @@ func (plan *wrapPtrArrayReflectScanPlan) Scan(src []byte, target any) error {
 	return plan.next.Scan(src, &anyArrayArrayReflect{array: reflect.ValueOf(target).Elem()})
 }
 
+type NilHandler func(*driver.NamedValue) error
+
+func (m *Map) TryNilHandling(nv *driver.NamedValue) error {
+	for _, f := range m.NilHandlers {
+		if err := f(nv); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // PlanScan prepares a plan to scan a value into target.
 func (m *Map) PlanScan(oid uint32, formatCode int16, target any) ScanPlan {
 	oidMemo := m.memoizedScanPlans[oid]

stdlib/sql.go

@@ -81,6 +81,7 @@ import (
 	"time"
 
 	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/internal/anynil"
 	"github.com/jackc/pgx/v5/pgconn"
 	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/jackc/pgx/v5/pgxpool"
@@ -533,8 +534,15 @@ func (c *Conn) Ping(ctx context.Context) error {
 	return nil
 }
 
-func (c *Conn) CheckNamedValue(*driver.NamedValue) error {
-	// Underlying pgx supports sql.Scanner and driver.Valuer interfaces natively. So everything can be passed through directly.
+func (c *Conn) CheckNamedValue(nv *driver.NamedValue) error {
+	// Underlying pgx supports sql.Scanner and driver.Valuer interfaces natively. If the Value itself is not nil, but
+	// can be considered nil, check to see if an option has been set up to handle it explicitly
+	if nv.Value != nil && anynil.Is(nv.Value) {
+		tm := c.conn.TypeMap()
+		if err := tm.TryNilHandling(nv); err != nil {
+			return err
+		}
+	}
 	return nil
 }