聊聊dbsync的Criterion

序

本文主要研究一下dbsync的Criterion

Criterion

//Criterion represents criterion
type Criterion fmt.Stringer

Criterion是一個fmt.Stringer類型

between

type between struct {
    from int
    to   int
}

func (b between) String() string {
    return fmt.Sprintf("BETWEEN %v AND %v", b.from, b.to)
}

//NewBetween creates new betwee criterion
func NewBetween(from, to int) Criterion {
    return &between{from: from, to: to}
}

between定義from、to兩個屬性

lessOrEqual

type lessOrEqual struct {
    value int
}

func (c lessOrEqual) String() string {
    return fmt.Sprintf(" <= %v", c.value)
}

//NewLessOrEqual creates less of equal criterion
func NewLessOrEqual(value int) Criterion {
    return &lessOrEqual{value}
}

lessOrEqual定義了value屬性，表達式爲 <=

greaterThan

type greaterThan struct {
    value int
}

func (c greaterThan) String() string {
    return fmt.Sprintf(" > %v", c.value)
}

//NewGraterThan creates grater than criterion
func NewGraterThan(value int) Criterion {
    return &greaterThan{value}
}

greaterThan定義了value屬性，表達式爲 >

greaterOrEqual

type greaterOrEqual struct {
    value int
}

func (c greaterOrEqual) String() string {
    return fmt.Sprintf(" >= %v", c.value)
}

//NewGraterOrEqual creates grater or equal criterion
func NewGraterOrEqual(value int) Criterion {
    return &greaterOrEqual{value}
}

greaterOrEqual定義了value屬性，表達式爲 >=

ToCriterion

//ToCriterion converts a kv pair to a criterion
func ToCriterion(k string, v interface{}) string {
    if greaterOrEqual, ok := v.(*greaterOrEqual); ok {
        return fmt.Sprintf("%v >= %v", k, greaterOrEqual.value)
    } else if greaterThan, ok := v.(*greaterThan); ok {
        return fmt.Sprintf("%v > %v", k, greaterThan.value)
    } else if lessOrEqual, ok := v.(*lessOrEqual); ok {
        return fmt.Sprintf("%v <= %v", k, lessOrEqual.value)
    } else if between, ok := v.(*between); ok {
        return fmt.Sprintf("%v BETWEEN %v AND %v", k, between.from, between.to)
    } else if toolbox.IsSlice(v) {
        aSlice := toolbox.AsSlice(v)
        var whereValues = make([]string, 0)
        for _, item := range aSlice {
            if intValue, err := toolbox.ToInt(item); err == nil {
                whereValues = append(whereValues, fmt.Sprintf(`%v`, intValue))
            } else {
                itemLiteral := toolbox.AsString(item)
                if strings.HasPrefix(itemLiteral, "(") && strings.HasSuffix(itemLiteral, ")") {
                    whereValues = append(whereValues, fmt.Sprintf(`%v`, item))
                } else {
                    whereValues = append(whereValues, fmt.Sprintf(`'%v'`, item))
                }
            }
        }
        return fmt.Sprintf("%v IN(%v)", k, strings.Join(whereValues, ","))
    } else if _, err := toolbox.ToInt(v); err == nil {
        return fmt.Sprintf("%v = %v", k, v)
    } else {
        literal := strings.TrimSpace(toolbox.AsString(v))
        lowerLiteral := strings.ToLower(literal)
        if strings.Contains(literal, ">") ||
            strings.Contains(literal, "<") ||
            strings.Contains(lowerLiteral, " null") {
            return fmt.Sprintf("%v %v", k, v)
        }
        return fmt.Sprintf("%v = '%v'", k, v)
    }
}

ToCriterion方法判斷v是不是greaterOrEqual、greaterThan、lessOrEqual、between類型作對應的轉換，針對IsSlice的作專門的拼接處理

小結

dbsync的Criterion是一個fmt.Stringer類型，它內置了greaterOrEqual、greaterThan、lessOrEqual、between類型，並提供ToCriterion方法進行轉換。

doc

• dbsync