codegen: don't auto-timestamp overwrite provided timestamps if there are ones

pkg/codegen/modelgenerate/generate_model.go

@@ -403,10 +403,21 @@ func GenerateSaveItemFunc(tbl schema.Table) *ast.FuncDecl {
 								ret1 := []ast.Stmt{Comment("Do create")}
 								if hasCreatedAt {
 									// Auto-timestamps: created_at
-									ret1 = append(ret1, &ast.AssignStmt{
+									ret1 = append(ret1, &ast.IfStmt{
+										// Don't overwrite existing timestamps.  This is useful for various reasons, e.g., data import / migrations
+										Cond: &ast.CallExpr{Fun: &ast.SelectorExpr{
+											X:   &ast.SelectorExpr{X: ast.NewIdent(tbl.VarName), Sel: ast.NewIdent("CreatedAt")},
+											Sel: ast.NewIdent("IsZero"),
+										}},
+										Body: &ast.BlockStmt{
+											List: []ast.Stmt{
+												&ast.AssignStmt{
 													Lhs: []ast.Expr{&ast.SelectorExpr{X: ast.NewIdent(tbl.VarName), Sel: ast.NewIdent("CreatedAt")}},
 													Tok: token.ASSIGN,
 													Rhs: []ast.Expr{&ast.CallExpr{Fun: ast.NewIdent("TimestampNow"), Args: []ast.Expr{}}},
+												},
+											},
+										},
 									})
 								}
 								return append(ret1, namedExecStmt(insertStmt)...)