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predicate.go
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predicate.go
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package lorm
// op 代表操作符
type op string
// 后面可以每次支持新的操作符就加一个
const (
opEQ = "="
opLT = "<"
opGT = ">"
opAND = "AND"
opOR = "OR"
opNOT = "NOT"
opAdd = "+"
opMulti = "*"
opExist = "EXIST"
opIN = "IN"
)
func (o op) String() string {
return string(o)
}
// Expression 代表语句,或者语句的部分
type Expression interface {
expr()
}
func exprOf(e any) Expression {
switch exp := e.(type) {
case Expression:
return exp
default:
return valueOf(exp)
}
}
// Predicate 代表一个查询条件
// Predicate 可以通过和 Predicate 组合构成复杂的查询条件
type Predicate struct {
left Expression
op op
right Expression
}
func (Predicate) expr() {}
func Not(p Predicate) Predicate {
return Predicate{
op: opNOT,
right: p,
}
}
func (p Predicate) And(r Predicate) Predicate {
return Predicate{
left: p,
op: opAND,
right: r,
}
}
func (p Predicate) Or(right Predicate) Predicate {
return Predicate{
left: p,
op: opOR,
right: right,
}
}
func Exist(sub Subquery) Predicate {
return Predicate{
op: opExist,
right: sub,
}
}