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本文次要钻研一下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 clausefunc (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 clausesfunc (onConflict OnConflict) MergeClause(clause *Clause) { clause.Expression = onConflict}OnConflict定义了Columns、Where、OnConstraint、DoNothing、DoUpdates、UpdateAll属性；Build办法会依据这些属性拼装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 []Assignmenttype 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 clausesfunc (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类型理论是Assignment数组；其Build办法会组装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) }}输入
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.id2021/01/17 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小结
gorm的OnConflict定义了Columns、Where、OnConstraint、DoNothing、DoUpdates、UpdateAll属性；Build办法会依据这些属性拼装sql，如果是DoNothing则追加DO NOTHING，否则追加DO UPDATE SET。
doc
- gorm