Huangzj
57 lines
1.6 KiB
Go
57 lines
1.6 KiB
Go
package linq
|
|
|
|
// Join correlates the elements of two collection based on matching keys.
|
|
//
|
|
// A join refers to the operation of correlating the elements of two sources
|
|
// of information based on a common key. Join brings the two information sources
|
|
// and the keys by which they are matched together in one method call.
|
|
// This differs from the use of SelectMany, which requires more than one method call
|
|
// to perform the same operation.
|
|
//
|
|
// Join preserves the order of the elements of outer collection,
|
|
// and for each of these elements, the order of the matching elements of inner.
|
|
func (q Query) Join(
|
|
inner Query,
|
|
outerKeySelector func(interface{}) interface{},
|
|
innerKeySelector func(interface{}) interface{},
|
|
resultSelector func(outer interface{}, inner interface{}) interface{},
|
|
) Query {
|
|
|
|
return Query{
|
|
Iterate: func() Iterator {
|
|
outernext := q.Iterate()
|
|
innernext := inner.Iterate()
|
|
|
|
innerLookup := make(map[interface{}][]interface{})
|
|
for innerItem, ok := innernext(); ok; innerItem, ok = innernext() {
|
|
innerKey := innerKeySelector(innerItem)
|
|
innerLookup[innerKey] = append(innerLookup[innerKey], innerItem)
|
|
}
|
|
|
|
var outerItem interface{}
|
|
var innerGroup []interface{}
|
|
innerLen, innerIndex := 0, 0
|
|
|
|
return func() (item interface{}, ok bool) {
|
|
if innerIndex >= innerLen {
|
|
has := false
|
|
for !has {
|
|
outerItem, ok = outernext()
|
|
if !ok {
|
|
return
|
|
}
|
|
|
|
innerGroup, has = innerLookup[outerKeySelector(outerItem)]
|
|
innerLen = len(innerGroup)
|
|
innerIndex = 0
|
|
}
|
|
}
|
|
|
|
item = resultSelector(outerItem, innerGroup[innerIndex])
|
|
innerIndex++
|
|
return item, true
|
|
}
|
|
},
|
|
}
|
|
}
|