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本文主要研究一下gorm的GroupBy

GroupBy

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

// GroupBy group by clause
type GroupBy struct {
	Columns []Column
	Having  []Expression
}

// Name from clause name
func (groupBy GroupBy) Name() string {
	return "GROUP BY"
}

// Build build group by clause
func (groupBy GroupBy) Build(builder Builder) {
	for idx, column := range groupBy.Columns {
		if idx > 0 {
			builder.WriteByte(',')
		}

		builder.WriteQuoted(column)
	}

	if len(groupBy.Having) > 0 {
		builder.WriteString(" HAVING ")
		Where{Exprs: groupBy.Having}.Build(builder)
	}
}

// MergeClause merge group by clause
func (groupBy GroupBy) MergeClause(clause *Clause) {
	if v, ok := clause.Expression.(GroupBy); ok {
		copiedColumns := make([]Column, len(v.Columns))
		copy(copiedColumns, v.Columns)
		groupBy.Columns = append(copiedColumns, groupBy.Columns...)

		copiedHaving := make([]Expression, len(v.Having))
		copy(copiedHaving, v.Having)
		groupBy.Having = append(copiedHaving, groupBy.Having...)
	}
	clause.Expression = groupBy
}
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GroupBy定义了Columns和Having属性，其Build方法遍历Columns，最后针对Having在拼接Having子句

实例

func TestGroupBy(t *testing.T) {
	results := []struct {
		Clauses []clause.Interface
		Result  string
		Vars    []interface{}
	}{
		{
			[]clause.Interface{clause.Select{}, clause.From{}, clause.GroupBy{
				Columns: []clause.Column{{Name: "role"}},
				Having:  []clause.Expression{clause.Eq{"role", "admin"}},
			}},
			"SELECT * FROM `users` GROUP BY `role` HAVING `role` = ?", []interface{}{"admin"},
		},
		{
			[]clause.Interface{clause.Select{}, clause.From{}, clause.GroupBy{
				Columns: []clause.Column{{Name: "role"}},
				Having:  []clause.Expression{clause.Eq{"role", "admin"}},
			}, clause.GroupBy{
				Columns: []clause.Column{{Name: "gender"}},
				Having:  []clause.Expression{clause.Neq{"gender", "U"}},
			}},
			"SELECT * FROM `users` GROUP BY `role`,`gender` HAVING `role` = ? AND `gender` <> ?", []interface{}{"admin", "U"},
		},
	}

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

gorm的GroupBy定义了Columns和Having属性，其Build方法遍历Columns，最后针对Having在拼接Having子句。

doc

• gorm