Remove duplicated mangas from gql "mangas" query

server/src/main/kotlin/suwayomi/tachidesk/graphql/queries/MangaQuery.kt

@@ -28,6 +28,7 @@ import suwayomi.tachidesk.graphql.queries.filter.andFilterWithCompare
 import suwayomi.tachidesk.graphql.queries.filter.andFilterWithCompareEntity
 import suwayomi.tachidesk.graphql.queries.filter.andFilterWithCompareString
 import suwayomi.tachidesk.graphql.queries.filter.applyOps
+import suwayomi.tachidesk.graphql.queries.util.distinctOn
 import suwayomi.tachidesk.graphql.server.primitives.Cursor
 import suwayomi.tachidesk.graphql.server.primitives.OrderBy
 import suwayomi.tachidesk.graphql.server.primitives.PageInfo
@@ -217,7 +218,12 @@ class MangaQuery {
     ): MangaNodeList {
         val queryResults =
             transaction {
-                val res = MangaTable.leftJoin(CategoryMangaTable).selectAll()
+                val res =
+                    MangaTable.leftJoin(CategoryMangaTable).slice(
+                        distinctOn(MangaTable.id),
+                        *(MangaTable.columns).toTypedArray(),
+                        *(CategoryMangaTable.columns).toTypedArray(),
+                    ).selectAll()
 
                 res.applyOps(condition, filter)
 

server/src/main/kotlin/suwayomi/tachidesk/graphql/queries/util/CustomDistinctOn.kt

@@ -0,0 +1,31 @@
+package suwayomi.tachidesk.graphql.queries.util
+
+import org.jetbrains.exposed.sql.BooleanColumnType
+import org.jetbrains.exposed.sql.CustomFunction
+import org.jetbrains.exposed.sql.Expression
+import org.jetbrains.exposed.sql.QueryBuilder
+
+/**
+ * src: https://github.com/JetBrains/Exposed/issues/500#issuecomment-543574151 (2024-04-02 02:20)
+ */
+
+fun distinctOn(vararg expressions: Expression<*>): CustomFunction<Boolean?> =
+    customBooleanFunction(
+        functionName = "DISTINCT ON",
+        postfix = " TRUE",
+        params = expressions,
+    )
+
+fun customBooleanFunction(
+    functionName: String,
+    postfix: String = "",
+    vararg params: Expression<*>,
+): CustomFunction<Boolean?> =
+    object : CustomFunction<Boolean?>(functionName, BooleanColumnType(), *params) {
+        override fun toQueryBuilder(queryBuilder: QueryBuilder) {
+            super.toQueryBuilder(queryBuilder)
+            if (postfix.isNotEmpty()) {
+                queryBuilder.append(postfix)
+            }
+        }
+    }