聊聊gorm的Locking

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本文主要研究一下gorm的Locking

Locking

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

type Locking struct {
	Strength string
	Table    Table
	Options  string
}

// Name where clause name
func (locking Locking) Name() string {
	return "FOR"
}

// Build build where clause
func (locking Locking) Build(builder Builder) {
	builder.WriteString(locking.Strength)
	if locking.Table.Name != "" {
		builder.WriteString(" OF ")
		builder.WriteQuoted(locking.Table)
	}

	if locking.Options != "" {
		builder.WriteByte(' ')
		builder.WriteString(locking.Options)
	}
}

// MergeClause merge order by clauses
func (locking Locking) MergeClause(clause *Clause) {
	clause.Expression = locking
}

Locking定义了Strength、Table、Options属性;Build方法先追加Strength,后面根据Table、Options属性追加语句

实例

func TestLocking(t *testing.T) {
	results := []struct {
		Clauses []clause.Interface
		Result  string
		Vars    []interface{}
	}{
		{
			[]clause.Interface{clause.Select{}, clause.From{}, clause.Locking{Strength: "UPDATE"}},
			"SELECT * FROM `users` FOR UPDATE", nil,
		},
		{
			[]clause.Interface{clause.Select{}, clause.From{}, clause.Locking{Strength: "SHARE", Table: clause.Table{Name: clause.CurrentTable}}},
			"SELECT * FROM `users` FOR SHARE OF `users`", nil,
		},
		{
			[]clause.Interface{clause.Select{}, clause.From{}, clause.Locking{Strength: "UPDATE"}, clause.Locking{Strength: "UPDATE", Options: "NOWAIT"}},
			"SELECT * FROM `users` FOR UPDATE NOWAIT", nil,
		},
	}

	for idx, result := range results {
		t.Run(fmt.Sprintf("case #%v", idx), func(t *testing.T) {
			checkBuildClauses(t, result.Clauses, result.Result, result.Vars)
		})
	}
}

小结

Locking定义了Strength、Table、Options属性;Build方法先追加Strength,后面根据Table、Options属性追加语句;Strength支持SHARE、UPDATE;Options支持NOWAIT。

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