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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
}

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)
        })
    }
}

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