聊聊gorm的OnConflict

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本文深入解析了gorm库中OnConflict功能的实现原理及其使用方法。详细介绍了OnConflict结构体的各项属性，包括Columns、Where、OnConstraint等，并通过具体示例展示了如何在实际应用中运用这些属性来构建SQL语句。

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序

本文主要研究一下gorm的OnConflict

OnConflict

gorm.io/gorm@v1.20.11/clause/on_conflict.go

type OnConflict struct {
	Columns      []Column
	Where        Where
	OnConstraint string
	DoNothing    bool
	DoUpdates    Set
	UpdateAll    bool
}

func (OnConflict) Name() string {
	return "ON CONFLICT"
}

// Build build onConflict clause
func (onConflict OnConflict) Build(builder Builder) {
	if len(onConflict.Columns) > 0 {
		builder.WriteByte('(')
		for idx, column := range onConflict.Columns {
			if idx > 0 {
				builder.WriteByte(',')
			}
			builder.WriteQuoted(column)
		}
		builder.WriteString(`) `)
	}

	if len(onConflict.Where.Exprs) > 0 {
		builder.WriteString("WHERE ")
		onConflict.Where.Build(builder)
		builder.WriteByte(' ')
	}

	if onConflict.OnConstraint != "" {
		builder.WriteString("ON CONSTRAINT ")
		builder.WriteString(onConflict.OnConstraint)
		builder.WriteByte(' ')
	}

	if onConflict.DoNothing {
		builder.WriteString("DO NOTHING")
	} else {
		builder.WriteString("DO UPDATE SET ")
		onConflict.DoUpdates.Build(builder)
	}
}

// MergeClause merge onConflict clauses
func (onConflict OnConflict) MergeClause(clause *Clause) {
	clause.Expression = onConflict
}

OnConflict定义了Columns、Where、OnConstraint、DoNothing、DoUpdates、UpdateAll属性；Build方法会根据这些属性拼装sql，如果是DoNothing则追加DO NOTHING，否则追加DO UPDATE SET

Expression

gorm.io/gorm@v1.20.11/clause/set.go

type Set []Assignment

type Assignment struct {
	Column Column
	Value  interface{}
}

func (set Set) Name() string {
	return "SET"
}

func (set Set) Build(builder Builder) {
	if len(set) > 0 {
		for idx, assignment := range set {
			if idx > 0 {
				builder.WriteByte(',')
			}
			builder.WriteQuoted(assignment.Column)
			builder.WriteByte('=')
			builder.AddVar(builder, assignment.Value)
		}
	} else {
		builder.WriteQuoted(PrimaryColumn)
		builder.WriteByte('=')
		builder.WriteQuoted(PrimaryColumn)
	}
}

// MergeClause merge assignments clauses
func (set Set) MergeClause(clause *Clause) {
	copiedAssignments := make([]Assignment, len(set))
	copy(copiedAssignments, set)
	clause.Expression = Set(copiedAssignments)
}

func Assignments(values map[string]interface{}) Set {
	keys := make([]string, 0, len(values))
	for key := range values {
		keys = append(keys, key)
	}
	sort.Strings(keys)

	assignments := make([]Assignment, len(keys))
	for idx, key := range keys {
		assignments[idx] = Assignment{Column: Column{Name: key}, Value: values[key]}
	}
	return assignments
}

func AssignmentColumns(values []string) Set {
	assignments := make([]Assignment, len(values))
	for idx, value := range values {
		assignments[idx] = Assignment{Column: Column{Name: value}, Value: Column{Table: "excluded", Name: value}}
	}
	return assignments
}

的DoUpdates属性是Set类型，Set类型实际是Assignment数组；其Build方法会组装assignment的sql

实例

func onConflictDemo(db *gorm.DB) {
	entities := []DemoEntity{
		{
			Model: gorm.Model{ID: 1},
			Name:  "coco",
		},
		{
			Model: gorm.Model{ID: 2},
			Name:  "bear",
		},
	}
	result := db.Debug().Create(&entities)
	b, _ := json.Marshal(entities)
	log.Println("data:", string(b))
	log.Println("result.RowsAffected:", result.RowsAffected, "result.Error:", result.Error)

	if err := db.Debug().Clauses(clause.OnConflict{DoNothing: true}).Create(&entities).Error; err != nil {
		panic(err)
	}
}

输出

2021/01/17 20:03:31 /demo.go:53 UNIQUE constraint failed: demo_entities.id
[0.487ms] [rows:0] INSERT INTO `demo_entities` (`created_at`,`updated_at`,`deleted_at`,`name`,`id`) VALUES ("2021-01-17 20:03:31.711","2021-01-17 20:03:31.711",NULL,"coco",1),("2021-01-17 20:03:31.711","2021-01-17 20:03:31.711",NULL,"bear",2)
2021/01/17 20:03:31 data: [{"ID":1,"CreatedAt":"2021-01-17T20:03:31.71143+08:00","UpdatedAt":"2021-01-17T20:03:31.71143+08:00","DeletedAt":null,"Name":"coco"},{"ID":2,"CreatedAt":"2021-01-17T20:03:31.71143+08:00","UpdatedAt":"2021-01-17T20:03:31.71143+08:00","DeletedAt":null,"Name":"bear"}]
2021/01/17 20:03:31 result.RowsAffected: 0 result.Error: UNIQUE constraint failed: demo_entities.id

2021/01/17 20:03:31 /demo.go:58
[0.123ms] [rows:0] INSERT INTO `demo_entities` (`created_at`,`updated_at`,`deleted_at`,`name`,`id`) VALUES ("2021-01-17 20:03:31.711","2021-01-17 20:03:31.711",NULL,"coco",1),("2021-01-17 20:03:31.711","2021-01-17 20:03:31.711",NULL,"bear",2) ON CONFLICT DO NOTHING