本文主要研究一下dbsync的Criterion
//Criterion represents criterion
type Criterion fmt.Stringer
Criterion是一个fmt.Stringer类型
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定义from、to两个属性
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定义了value属性,表达式为<=
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定义了value属性,表达式为>
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定义了value属性,表达式为>=
//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的做专门的拼接处理
dbsync的Criterion是一个fmt.Stringer类型,它内置了greaterOrEqual、greaterThan、lessOrEqual、between类型,并提供ToCriterion方法进行转换。
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