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本文次要钻研一下dbsync的Criterion

Criterion

//Criterion represents criteriontype Criterion fmt.Stringer
Criterion是一个fmt.Stringer类型

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 criterionfunc NewBetween(from, to int) Criterion {    return &between{from: from, to: to}}
between定义from、to两个属性

lessOrEqual

type lessOrEqual struct {    value int}func (c lessOrEqual) String() string {    return fmt.Sprintf(" <= %v", c.value)}//NewLessOrEqual creates less of equal criterionfunc NewLessOrEqual(value int) Criterion {    return &lessOrEqual{value}}
lessOrEqual定义了value属性，表达式为<=

greaterThan

type greaterThan struct {    value int}func (c greaterThan) String() string {    return fmt.Sprintf(" > %v", c.value)}//NewGraterThan creates grater than criterionfunc NewGraterThan(value int) Criterion {    return &greaterThan{value}}
greaterThan定义了value属性，表达式为>

greaterOrEqual

type greaterOrEqual struct {    value int}func (c greaterOrEqual) String() string {    return fmt.Sprintf(" >= %v", c.value)}//NewGraterOrEqual creates grater or equal criterionfunc NewGraterOrEqual(value int) Criterion {    return &greaterOrEqual{value}}
greaterOrEqual定义了value属性，表达式为>=

ToCriterion

//ToCriterion converts a kv pair to a criterionfunc 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办法判断v是否是greaterOrEqual、greaterThan、lessOrEqual、between类型做对应的转换，针对IsSlice的做专门的拼接解决

小结

dbsync的Criterion是一个fmt.Stringer类型，它内置了greaterOrEqual、greaterThan、lessOrEqual、between类型，并提供ToCriterion办法进行转换。

doc

  • dbsync