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aggregation.go
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/
aggregation.go
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package norm
import (
"context"
"fmt"
)
type Merge[M1, M2 any] struct {
L M1
R []M2
}
type Keyer[K comparable] interface {
Key() K
}
// Lookup performs left outer join.
func Lookup[
M1 ~[]T1,
M2 ~[]T2,
T1, T2 Keyer[K],
A1, A2 any,
K comparable,
](
ctx context.Context,
lhs Reader[M1, A1], lhsArgs A1,
rhs Reader[M2, A2], rhsArgs A2,
) (
merge []Merge[T1, T2],
err error,
) {
l, err := lhs.Read(ctx, lhsArgs)
if err != nil {
return nil, fmt.Errorf("read lhs: %w", err)
}
r, err := rhs.Read(ctx, rhsArgs)
if err != nil {
return nil, fmt.Errorf("read rhs: %w", err)
}
return _lookup[M1, M2, T1, T2, K](l, r), nil
}
// Group performs values grouping.
func Group[
M ~[]T,
T Keyer[K],
A any,
K comparable,
](
ctx context.Context,
r Reader[M, A],
args A,
) (
groups map[K][]T,
err error,
) {
values, err := r.Read(ctx, args)
if err != nil {
return nil, fmt.Errorf("read lhs: %w", err)
}
return _group[M, T, K](values)
}
func _lookup[
M1 ~[]T1,
M2 ~[]T2,
T1 Keyer[K],
T2 Keyer[K],
K comparable,
](
lhs M1,
rhs M2,
) (
out []Merge[T1, T2],
) {
out = make([]Merge[T1, T2], 0, len(lhs))
m := make(map[K][]int, len(rhs))
for i, v := range rhs {
k := v.Key()
m[k] = append(m[k], i)
}
for _, l := range lhs {
merge := Merge[T1, T2]{
L: l,
R: nil,
}
rii, ok := m[l.Key()]
if ok {
for _, i := range rii {
merge.R = append(merge.R, rhs[i])
}
}
out = append(out, merge)
}
return out
}
func _group[
M ~[]T,
T Keyer[K],
K comparable,
](
values M,
) (
groups map[K][]T,
err error,
) {
groups = make(map[K][]T, len(values))
for _, v := range values {
k := v.Key()
groups[k] = append(groups[k], v)
}
return
}