docs: Add CLAUDE.md with codebase guidance

Create comprehensive documentation for future Claude Code instances working in this repository, including:
- Development commands for testing, building, and code quality
- Core architecture overview of the SQL query builder system
- Directory structure and component explanations
- Testing patterns and conventions
- Key dependencies and their purposes

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/util/reflect.go

@@ -2,11 +2,12 @@ package util
 
 import (
 	"database/sql"
+	"encoding/json"
 	"reflect"
 	"strings"
 	"sync"
 
-	"git.fsdpf.net/go/db/v2/internal/errors"
+	"git.fsdpf.net/go/db/internal/errors"
 )
 
 const (
@@ -56,6 +57,10 @@ func IsStruct(k reflect.Kind) bool {
 	return k == reflect.Struct
 }
 
+func IsMap(k reflect.Kind) bool {
+	return k == reflect.Map
+}
+
 func IsInvalid(k reflect.Kind) bool {
 	return k == reflect.Invalid
 }
@@ -117,6 +122,15 @@ func GetSliceElementType(val reflect.Value) reflect.Type {
 	return elemType
 }
 
+func GetMapElementType(val reflect.Value) reflect.Type {
+	elemType := val.Type().Elem()
+	if elemType.Kind() == reflect.Ptr {
+		elemType = elemType.Elem()
+	}
+
+	return elemType
+}
+
 // AppendSliceElement will append val to slice. Handles slice of pointers and
 // not pointers. Val needs to be a pointer.
 func AppendSliceElement(slice, val reflect.Value) {
@@ -167,16 +181,8 @@ func SafeSetFieldByIndex(v reflect.Value, fieldIndex []int, src interface{}) (re
 		return v
 	case 1:
 		f := v.FieldByIndex(fieldIndex)
-		srcVal := reflect.ValueOf(src).Elem()
-		// 处理 converting NULL to string is unsupported
-		// 前面将 string 和 int 类型转为了 *string 和 *int
-		// 这里做还原
-		if srcVal.IsNil() {
-			f.Set(reflect.Zero(f.Type()))
-		} else if f.Type().ConvertibleTo(srcVal.Type().Elem()) {
-			f.Set(srcVal.Elem())
-		} else {
-			f.Set(srcVal)
+		if err := SafeSetVarValue(f, src); err != nil {
+			panic(err)
 		}
 	default:
 		f := v.Field(fieldIndex[0])
@@ -196,6 +202,28 @@ func SafeSetFieldByIndex(v reflect.Value, fieldIndex []int, src interface{}) (re
 	return v
 }
 
+func SafeSetVarValue(v reflect.Value, src interface{}) error {
+	f := reflect.Indirect(v)
+	srcVal := reflect.ValueOf(src).Elem()
+
+	// 处理 converting NULL to string is unsupported
+	// 前面将 string 和 int 类型转为了 *string 和 *int
+	// 这里做还原
+	if srcVal.IsNil() {
+		f.Set(reflect.Zero(f.Type()))
+	} else if f.Type().ConvertibleTo(srcVal.Type().Elem()) {
+		f.Set(srcVal.Elem())
+	} else if f.Type().ConvertibleTo(srcVal.Type()) {
+		f.Set(srcVal)
+	} else if u, ok := srcVal.Interface().(*json.RawMessage); ok && len(*u) >= 2 {
+		if err := json.Unmarshal(*u, f.Addr().Interface()); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 type rowData = map[string]interface{}
 
 // AssignStructVals will assign the data from rd to i.