Migration: refactor output/processing of converted entities

This commit simplifies the `icingaDbOutputStage` type to contain only one
entity slice to be insert/upsert. This allows to simplify the handling in
`migrateOneType()` by removing nested loops.

Additionally, a bit of code inside that function is outsourced into a new
`utils.ChanFromSlice()` function. This makes the body of the loop over the
insert/upsert operation (the loop using the `op` variable) simple enough so
that it can just be unrolled which saves the inline struct and slice definition
for that loop.

cmd/icingadb-migrate/convert.go

@@ -207,9 +207,12 @@ func convertCommentRows(
 		}
 	}
 
-	stages = []icingaDbOutputStage{{inserts: [][]contracts.Entity{
-		commentHistory, acknowledgementHistory, allHistoryComment, allHistoryAck,
-	}}}
+	stages = []icingaDbOutputStage{
+		{insert: commentHistory},
+		{insert: acknowledgementHistory},
+		{insert: allHistoryComment},
+		{insert: allHistoryAck},
+	}
 	return
 }
 
@@ -359,7 +362,11 @@ func convertDowntimeRows(
 		sla = append(sla, s)
 	}
 
-	stages = []icingaDbOutputStage{{inserts: [][]contracts.Entity{downtimeHistory, allHistory, sla}}}
+	stages = []icingaDbOutputStage{
+		{insert: downtimeHistory},
+		{insert: allHistory},
+		{insert: sla},
+	}
 	return
 }
 
@@ -509,11 +516,9 @@ func convertFlappingRows(
 	}
 
 	stages = []icingaDbOutputStage{
-		{
-			inserts: [][]contracts.Entity{flappingHistory},
-			upserts: [][]contracts.Entity{flappingHistoryUpserts},
-		},
-		{inserts: [][]contracts.Entity{allHistory}},
+		{insert: flappingHistory},
+		{upsert: flappingHistoryUpserts},
+		{insert: allHistory},
 	}
 	return
 }
@@ -672,9 +677,11 @@ func convertNotificationRows(
 		}
 	}
 
-	stages = []icingaDbOutputStage{{inserts: [][]contracts.Entity{
-		notificationHistory, userNotificationHistory, allHistory,
-	}}}
+	stages = []icingaDbOutputStage{
+		{insert: notificationHistory},
+		{insert: userNotificationHistory},
+		{insert: allHistory},
+	}
 	return
 }
 
@@ -828,6 +835,10 @@ func convertStateRows(
 		}
 	}
 
-	stages = []icingaDbOutputStage{{inserts: [][]contracts.Entity{stateHistory, allHistory, sla}}}
+	stages = []icingaDbOutputStage{
+		{insert: stateHistory},
+		{insert: allHistory},
+		{insert: sla},
+	}
 	return
 }

cmd/icingadb-migrate/main.go

@@ -9,7 +9,6 @@ import (
 	"github.com/creasty/defaults"
 	"github.com/goccy/go-yaml"
 	"github.com/icinga/icingadb/pkg/config"
-	"github.com/icinga/icingadb/pkg/contracts"
 	"github.com/icinga/icingadb/pkg/icingadb"
 	"github.com/icinga/icingadb/pkg/logging"
 	icingadbTypes "github.com/icinga/icingadb/pkg/types"
@@ -428,30 +427,21 @@ func migrateOneType[IdoRow any](
 			// ... and insert them:
 
 			for _, stage := range stages {
-				for _, op := range []struct {
-					kind     string
-					data     [][]contracts.Entity
-					streamer func(context.Context, <-chan contracts.Entity, ...icingadb.OnSuccess[contracts.Entity]) error
-				}{
-					{"INSERT IGNORE", stage.inserts, idb.CreateIgnoreStreamed},
-					{"UPSERT", stage.upserts, idb.UpsertStreamed},
-				} {
-					for _, table := range op.data {
-						if len(table) < 1 {
-							continue
-						}
-
-						ch := make(chan contracts.Entity, len(table))
-						for _, row := range table {
-							ch <- row
-						}
-
-						close(ch)
-
-						if err := op.streamer(context.Background(), ch); err != nil {
-							log.With("backend", "Icinga DB", "op", op.kind, "table", utils.TableName(table[0])).
-								Fatalf("%+v", errors.Wrap(err, "can't perform DML"))
-						}
+				if len(stage.insert) > 0 {
+					ch := utils.ChanFromSlice(stage.insert)
+
+					if err := idb.CreateIgnoreStreamed(context.Background(), ch); err != nil {
+						log.With("backend", "Icinga DB", "op", "INSERT IGNORE", "table", utils.TableName(stage.insert[0])).
+							Fatalf("%+v", errors.Wrap(err, "can't perform DML"))
+					}
+				}
+
+				if len(stage.upsert) > 0 {
+					ch := utils.ChanFromSlice(stage.upsert)
+
+					if err := idb.UpsertStreamed(context.Background(), ch); err != nil {
+						log.With("backend", "Icinga DB", "op", "UPSERT", "table", utils.TableName(stage.upsert[0])).
+							Fatalf("%+v", errors.Wrap(err, "can't perform DML"))
 					}
 				}
 			}

cmd/icingadb-migrate/misc.go

@@ -238,7 +238,7 @@ func (hts historyTypes) forEach(f func(*historyType)) {
 }
 
 type icingaDbOutputStage struct {
-	inserts, upserts [][]contracts.Entity
+	insert, upsert []contracts.Entity
 }
 
 var types = historyTypes{

pkg/utils/utils.go

@@ -216,3 +216,16 @@ func JoinHostPort(host string, port int) string {
 
 	return net.JoinHostPort(host, fmt.Sprint(port))
 }
+
+// ChanFromSlice takes a slice of values and returns a channel from which these values can be received.
+// This channel is closed after the last value was sent.
+func ChanFromSlice[T any](values []T) <-chan T {
+	ch := make(chan T, len(values))
+	for _, value := range values {
+		ch <- value
+	}
+
+	close(ch)
+
+	return ch
+}

pkg/utils/utils_test.go

@@ -0,0 +1,54 @@
+package utils
+
+import (
+	"github.com/stretchr/testify/require"
+	"testing"
+)
+
+func TestChanFromSlice(t *testing.T) {
+	t.Run("Nil", func(t *testing.T) {
+		ch := ChanFromSlice[int](nil)
+		require.NotNil(t, ch)
+		requireClosedEmpty(t, ch)
+	})
+
+	t.Run("Empty", func(t *testing.T) {
+		ch := ChanFromSlice([]int{})
+		require.NotNil(t, ch)
+		requireClosedEmpty(t, ch)
+	})
+
+	t.Run("NonEmpty", func(t *testing.T) {
+		ch := ChanFromSlice([]int{42, 23, 1337})
+		require.NotNil(t, ch)
+		requireReceive(t, ch, 42)
+		requireReceive(t, ch, 23)
+		requireReceive(t, ch, 1337)
+		requireClosedEmpty(t, ch)
+	})
+}
+
+// requireReceive is a helper function to check if a value can immediately be received from a channel.
+func requireReceive(t *testing.T, ch <-chan int, expected int) {
+	t.Helper()
+
+	select {
+	case v, ok := <-ch:
+		require.True(t, ok, "receiving should return a value")
+		require.Equal(t, expected, v)
+	default:
+		require.Fail(t, "receiving should not block")
+	}
+}
+
+// requireReceive is a helper function to check if the channel is closed and empty.
+func requireClosedEmpty(t *testing.T, ch <-chan int) {
+	t.Helper()
+
+	select {
+	case _, ok := <-ch:
+		require.False(t, ok, "receiving from channel should not return anything")
+	default:
+		require.Fail(t, "receiving should not block")
+	}
+}