GORM 支持复杂对象

GORM 默认支持的是 Go basic types，根据 A Tour of Go 可以知道 Go basic types 包括：

bool

string

int  int8  int16  int32  int64
uint uint8 uint16 uint32 uint64 uintptr

byte // alias for uint8

rune // alias for int32
     // represents a Unicode code point

float32 float64

complex64 complex128

可见 GORM 默认支持的 Go 类型远无法胜任日常的开发需求，例如常用的[][]byte，map[sring]T 等等，下面就是我在使用 GORM 中碰到的一个场景：

上面的问题就是 GORM 原生不支持数据类型导致的问题，GORM 框架针对这样的问题提供了两种解决方法：

1. 它通过提供了少量接口使用户能够为 GORM 定义支持的数据类型；
2. 它通过提供自定义数据类型库提供支持，例如：datatypes，pq；

GORM 数据类型库

datatypes

GORM 社区扩展支持的数据类型，它主要包括：

• JSON
• Date
• Time
• JSON_SET
• JSONType[T]
• JSONSlice[T]
• JSONArray

可以看出来 datatypes 是通过 json 数据来表示复杂数据结构的。

pq

Postgres 为 Go 实现的 Driver 库，里面支持 GORM 数据类型（Scanner、Valuer interface），主要包括：

• Hstore,

// Hstore is a wrapper for transferring Hstore values back and forth easily.
type Hstore struct {
	Map map[string]sql.NullString
}

• NullTime,

type NullTime struct {
	Time  time.Time
	Valid bool // Valid is true if Time is not NULL
}

• Array,

// Array returns the optimal driver.Valuer and sql.Scanner for an array or
// slice of any dimension.
//
// For example:
//  db.Query(`SELECT * FROM t WHERE id = ANY($1)`, pq.Array([]int{235, 401}))
//
//  var x []sql.NullInt64
//  db.QueryRow(`SELECT ARRAY[235, 401]`).Scan(pq.Array(&x))
//
// Scanning multi-dimensional arrays is not supported.  Arrays where the lower
// bound is not one (such as `[0:0]={1}') are not supported.
func Array(a interface{}) interface {
	driver.Valuer
	sql.Scanner
} {
	switch a := a.(type) {
	case []bool:
		return (*BoolArray)(&a)
	case []float64:
		return (*Float64Array)(&a)
	case []float32:
		return (*Float32Array)(&a)
	case []int64:
		return (*Int64Array)(&a)
	case []int32:
		return (*Int32Array)(&a)
	case []string:
		return (*StringArray)(&a)
	case [][]byte:
		return (*ByteaArray)(&a)

	case *[]bool:
		return (*BoolArray)(a)
	case *[]float64:
		return (*Float64Array)(a)
	case *[]float32:
		return (*Float32Array)(a)
	case *[]int64:
		return (*Int64Array)(a)
	case *[]int32:
		return (*Int32Array)(a)
	case *[]string:
		return (*StringArray)(a)
	case *[][]byte:
		return (*ByteaArray)(a)
	}
	return GenericArray{a}
}

GORM 自定义类型

当前 GORM 从三个维度支持数据类型自定义：

• 解析和保存数据到数据库（Scanner、Valuer ）
• 数据库字段（列）的数据库类型（GormDBDataTypeInterface 或 GormDataTypeInterface）
• 复杂数据类型读取或查询（clause.Expression）

如何通过这几个 interface 来实现的自定义数据类型有一个非常好的样例代码可以参考，如何实现 GORM 支持复杂对象本文就不赘述了，直接上代码：

package datatypes

import (
	"context"
	"database/sql/driver"
	"encoding/json"
	"errors"
	"fmt"
	"reflect"
	"strconv"
	"strings"
	"sync"

	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"
	"gorm.io/gorm/schema"
)

// JSON defined JSON data type, need to implements driver.Valuer, sql.Scanner interface
type JSON json.RawMessage

// Value return json value, implement driver.Valuer interface
func (j JSON) Value() (driver.Value, error) {
	if len(j) == 0 {
		return nil, nil
	}
	return string(j), nil
}

// Scan scan value into Jsonb, implements sql.Scanner interface
func (j *JSON) Scan(value interface{}) error {
	if value == nil {
		*j = JSON("null")
		return nil
	}
	var bytes []byte
	switch v := value.(type) {
	case []byte:
		if len(v) > 0 {
			bytes = make([]byte, len(v))
			copy(bytes, v)
		}
	case string:
		bytes = []byte(v)
	default:
		return errors.New(fmt.Sprint("Failed to unmarshal JSONB value:", value))
	}

	result := json.RawMessage(bytes)
	*j = JSON(result)
	return nil
}

// MarshalJSON to output non base64 encoded []byte
func (j JSON) MarshalJSON() ([]byte, error) {
	return json.RawMessage(j).MarshalJSON()
}

// UnmarshalJSON to deserialize []byte
func (j *JSON) UnmarshalJSON(b []byte) error {
	result := json.RawMessage{}
	err := result.UnmarshalJSON(b)
	*j = JSON(result)
	return err
}

func (j JSON) String() string {
	return string(j)
}

// GormDataType gorm common data type
func (JSON) GormDataType() string {
	return "json"
}

// GormDBDataType gorm db data type
func (JSON) GormDBDataType(db *gorm.DB, field *schema.Field) string {
	switch db.Dialector.Name() {
	case "sqlite":
		return "JSON"
	case "mysql":
		return "JSON"
	case "postgres":
		return "JSONB"
	}
	return ""
}

func (js JSON) GormValue(ctx context.Context, db *gorm.DB) clause.Expr {
	if len(js) == 0 {
		return gorm.Expr("NULL")
	}

	data, _ := js.MarshalJSON()

	switch db.Dialector.Name() {
	case "mysql":
		if v, ok := db.Dialector.(*mysql.Dialector); ok && !strings.Contains(v.ServerVersion, "MariaDB") {
			return gorm.Expr("CAST(? AS JSON)", string(data))
		}
	}

	return gorm.Expr("?", string(data))
}

// JSONQueryExpression json query expression, implements clause.Expression interface to use as querier
type JSONQueryExpression struct {
	column      string
	keys        []string
	hasKeys     bool
	equals      bool
	likes       bool
	equalsValue interface{}
	extract     bool
	path        string
}

// JSONQuery query column as json
func JSONQuery(column string) *JSONQueryExpression {
	return &JSONQueryExpression{column: column}
}

// Extract extract json with path
func (jsonQuery *JSONQueryExpression) Extract(path string) *JSONQueryExpression {
	jsonQuery.extract = true
	jsonQuery.path = path
	return jsonQuery
}

// HasKey returns clause.Expression
func (jsonQuery *JSONQueryExpression) HasKey(keys ...string) *JSONQueryExpression {
	jsonQuery.keys = keys
	jsonQuery.hasKeys = true
	return jsonQuery
}

// Keys returns clause.Expression
func (jsonQuery *JSONQueryExpression) Equals(value interface{}, keys ...string) *JSONQueryExpression {
	jsonQuery.keys = keys
	jsonQuery.equals = true
	jsonQuery.equalsValue = value
	return jsonQuery
}

// Likes return clause.Expression
func (jsonQuery *JSONQueryExpression) Likes(value interface{}, keys ...string) *JSONQueryExpression {
	jsonQuery.keys = keys
	jsonQuery.likes = true
	jsonQuery.equalsValue = value
	return jsonQuery
}

// Build implements clause.Expression
func (jsonQuery *JSONQueryExpression) Build(builder clause.Builder) {
	if stmt, ok := builder.(*gorm.Statement); ok {
		switch stmt.Dialector.Name() {
		case "mysql", "sqlite":
			switch {
			case jsonQuery.extract:
				builder.WriteString("JSON_EXTRACT(")
				builder.WriteQuoted(jsonQuery.column)
				builder.WriteByte(',')
				builder.AddVar(stmt, prefix+jsonQuery.path)
				builder.WriteString(")")
			case jsonQuery.hasKeys:
				if len(jsonQuery.keys) > 0 {
					builder.WriteString("JSON_EXTRACT(")
					builder.WriteQuoted(jsonQuery.column)
					builder.WriteByte(',')
					builder.AddVar(stmt, jsonQueryJoin(jsonQuery.keys))
					builder.WriteString(") IS NOT NULL")
				}
			case jsonQuery.equals:
				if len(jsonQuery.keys) > 0 {
					builder.WriteString("JSON_EXTRACT(")
					builder.WriteQuoted(jsonQuery.column)
					builder.WriteByte(',')
					builder.AddVar(stmt, jsonQueryJoin(jsonQuery.keys))
					builder.WriteString(") = ")
					if value, ok := jsonQuery.equalsValue.(bool); ok {
						builder.WriteString(strconv.FormatBool(value))
					} else {
						stmt.AddVar(builder, jsonQuery.equalsValue)
					}
				}
			case jsonQuery.likes:
				if len(jsonQuery.keys) > 0 {
					builder.WriteString("JSON_EXTRACT(")
					builder.WriteQuoted(jsonQuery.column)
					builder.WriteByte(',')
					builder.AddVar(stmt, jsonQueryJoin(jsonQuery.keys))
					builder.WriteString(") LIKE ")
					if value, ok := jsonQuery.equalsValue.(bool); ok {
						builder.WriteString(strconv.FormatBool(value))
					} else {
						stmt.AddVar(builder, jsonQuery.equalsValue)
					}
				}
			}
		case "postgres":
			switch {
			case jsonQuery.extract:
				builder.WriteString(fmt.Sprintf("json_extract_path_text(%v::json,", stmt.Quote(jsonQuery.column)))
				stmt.AddVar(builder, jsonQuery.path)
				builder.WriteByte(')')
			case jsonQuery.hasKeys:
				if len(jsonQuery.keys) > 0 {
					stmt.WriteQuoted(jsonQuery.column)
					stmt.WriteString("::jsonb")
					for _, key := range jsonQuery.keys[0 : len(jsonQuery.keys)-1] {
						stmt.WriteString(" -> ")
						stmt.AddVar(builder, key)
					}

					stmt.WriteString(" ? ")
					stmt.AddVar(builder, jsonQuery.keys[len(jsonQuery.keys)-1])
				}
			case jsonQuery.equals:
				if len(jsonQuery.keys) > 0 {
					builder.WriteString(fmt.Sprintf("json_extract_path_text(%v::json,", stmt.Quote(jsonQuery.column)))

					for idx, key := range jsonQuery.keys {
						if idx > 0 {
							builder.WriteByte(',')
						}
						stmt.AddVar(builder, key)
					}
					builder.WriteString(") = ")

					if _, ok := jsonQuery.equalsValue.(string); ok {
						stmt.AddVar(builder, jsonQuery.equalsValue)
					} else {
						stmt.AddVar(builder, fmt.Sprint(jsonQuery.equalsValue))
					}
				}
			case jsonQuery.likes:
				if len(jsonQuery.keys) > 0 {
					builder.WriteString(fmt.Sprintf("json_extract_path_text(%v::json,", stmt.Quote(jsonQuery.column)))

					for idx, key := range jsonQuery.keys {
						if idx > 0 {
							builder.WriteByte(',')
						}
						stmt.AddVar(builder, key)
					}
					builder.WriteString(") LIKE ")

					if _, ok := jsonQuery.equalsValue.(string); ok {
						stmt.AddVar(builder, jsonQuery.equalsValue)
					} else {
						stmt.AddVar(builder, fmt.Sprint(jsonQuery.equalsValue))
					}
				}
			}
		}
	}
}

// JSONOverlapsExpression JSON_OVERLAPS expression, implements clause.Expression interface to use as querier
type JSONOverlapsExpression struct {
	column clause.Expression
	val    string
}

// JSONOverlaps query column as json
func JSONOverlaps(column clause.Expression, value string) *JSONOverlapsExpression {
	return &JSONOverlapsExpression{
		column: column,
		val:    value,
	}
}

// Build implements clause.Expression
// only mysql support JSON_OVERLAPS
func (json *JSONOverlapsExpression) Build(builder clause.Builder) {
	if stmt, ok := builder.(*gorm.Statement); ok {
		switch stmt.Dialector.Name() {
		case "mysql":
			builder.WriteString("JSON_OVERLAPS(")
			json.column.Build(builder)
			builder.WriteString(",")
			builder.AddVar(stmt, json.val)
			builder.WriteString(")")
		}
	}
}

type columnExpression string

func Column(col string) columnExpression {
	return columnExpression(col)
}

func (col columnExpression) Build(builder clause.Builder) {
	if stmt, ok := builder.(*gorm.Statement); ok {
		switch stmt.Dialector.Name() {
		case "mysql", "sqlite", "postgres":
			builder.WriteString(stmt.Quote(string(col)))
		}
	}
}

const prefix = "$."

func jsonQueryJoin(keys []string) string {
	if len(keys) == 1 {
		return prefix + keys[0]
	}

	n := len(prefix)
	n += len(keys) - 1
	for i := 0; i < len(keys); i++ {
		n += len(keys[i])
	}

	var b strings.Builder
	b.Grow(n)
	b.WriteString(prefix)
	b.WriteString(keys[0])
	for _, key := range keys[1:] {
		b.WriteString(".")
		b.WriteString(key)
	}
	return b.String()
}

// JSONSetExpression json set expression, implements clause.Expression interface to use as updater
type JSONSetExpression struct {
	column     string
	path2value map[string]interface{}
	mutex      sync.RWMutex
}

// JSONSet update fields of json column
func JSONSet(column string) *JSONSetExpression {
	return &JSONSetExpression{column: column, path2value: make(map[string]interface{})}
}

// Set return clause.Expression.
//
//	{
//		"age": 20,
//		"name": "json-1",
//		"orgs": {"orga": "orgv"},
//		"tags": ["tag1", "tag2"]
//	}
//
//	// In MySQL/SQLite, path is `age`, `name`, `orgs.orga`, `tags[0]`, `tags[1]`.
//	DB.UpdateColumn("attr", JSONSet("attr").Set("orgs.orga", 42))
//
//	// In PostgreSQL, path is `{age}`, `{name}`, `{orgs,orga}`, `{tags, 0}`, `{tags, 1}`.
//	DB.UpdateColumn("attr", JSONSet("attr").Set("{orgs, orga}", "bar"))
func (jsonSet *JSONSetExpression) Set(path string, value interface{}) *JSONSetExpression {
	jsonSet.mutex.Lock()
	jsonSet.path2value[path] = value
	jsonSet.mutex.Unlock()
	return jsonSet
}

// Build implements clause.Expression
// support mysql, sqlite and postgres
func (jsonSet *JSONSetExpression) Build(builder clause.Builder) {
	if stmt, ok := builder.(*gorm.Statement); ok {
		switch stmt.Dialector.Name() {
		case "mysql":

			var isMariaDB bool
			if v, ok := stmt.Dialector.(*mysql.Dialector); ok {
				isMariaDB = strings.Contains(v.ServerVersion, "MariaDB")
			}

			builder.WriteString("JSON_SET(")
			builder.WriteQuoted(jsonSet.column)
			for path, value := range jsonSet.path2value {
				builder.WriteByte(',')
				builder.AddVar(stmt, prefix+path)
				builder.WriteByte(',')

				if _, ok := value.(clause.Expression); ok {
					stmt.AddVar(builder, value)
					continue
				}

				rv := reflect.ValueOf(value)
				if rv.Kind() == reflect.Ptr {
					rv = rv.Elem()
				}
				switch rv.Kind() {
				case reflect.Slice, reflect.Array, reflect.Struct, reflect.Map:
					b, _ := json.Marshal(value)
					if isMariaDB {
						stmt.AddVar(builder, string(b))
						break
					}
					stmt.AddVar(builder, gorm.Expr("CAST(? AS JSON)", string(b)))
				default:
					stmt.AddVar(builder, value)
				}
			}
			builder.WriteString(")")

		case "sqlite":
			builder.WriteString("JSON_SET(")
			builder.WriteQuoted(jsonSet.column)
			for path, value := range jsonSet.path2value {
				builder.WriteByte(',')
				builder.AddVar(stmt, prefix+path)
				builder.WriteByte(',')

				if _, ok := value.(clause.Expression); ok {
					stmt.AddVar(builder, value)
					continue
				}

				rv := reflect.ValueOf(value)
				if rv.Kind() == reflect.Ptr {
					rv = rv.Elem()
				}
				switch rv.Kind() {
				case reflect.Slice, reflect.Array, reflect.Struct, reflect.Map:
					b, _ := json.Marshal(value)
					stmt.AddVar(builder, gorm.Expr("JSON(?)", string(b)))
				default:
					stmt.AddVar(builder, value)
				}
			}
			builder.WriteString(")")

		case "postgres":
			var expr clause.Expression = columnExpression(jsonSet.column)
			for path, value := range jsonSet.path2value {
				if _, ok = value.(clause.Expression); ok {
					expr = gorm.Expr("JSONB_SET(?,?,?)", expr, path, value)
					continue
				} else {
					b, _ := json.Marshal(value)
					expr = gorm.Expr("JSONB_SET(?,?,?)", expr, path, string(b))
				}
			}
			stmt.AddVar(builder, expr)
		}
	}
}

func JSONArrayQuery(column string) *JSONArrayExpression {
	return &JSONArrayExpression{
		column: column,
	}
}

type JSONArrayExpression struct {
	column      string
	equalsValue interface{}
}

func (json *JSONArrayExpression) Contains(value interface{}) *JSONArrayExpression {
	json.equalsValue = value
	return json
}

// Build implements clause.Expression
func (json *JSONArrayExpression) Build(builder clause.Builder) {
	if stmt, ok := builder.(*gorm.Statement); ok {
		switch stmt.Dialector.Name() {
		case "mysql":
			builder.WriteString("JSON_CONTAINS (" + stmt.Quote(json.column) + ", JSON_ARRAY(")
			builder.AddVar(stmt, json.equalsValue)
			builder.WriteString("))")
		}
	}
}

References

1. lib/pq: Pure Go Postgres driver for database/sql
2. go-gorm/datatypes: GORM Customized Data Types Collection
3. Customize Data Types | GORM - The fantastic ORM library for Golang, aims to be developer friendly.