From 423d084defec3f80b368ce80d9ea4975b6e339da Mon Sep 17 00:00:00 2001
From: manelcecs <manuelc.p.g@gmail.com>
Date: Thu, 11 Jul 2024 09:57:18 +0200
Subject: [PATCH] Add 'distinct' clause

---
 src/db/util/raw-model.ts | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/src/db/util/raw-model.ts b/src/db/util/raw-model.ts
index 780f8e2c..ef66daa7 100644
--- a/src/db/util/raw-model.ts
+++ b/src/db/util/raw-model.ts
@@ -46,6 +46,16 @@ export type FindFn<F extends FieldDefinition, AdditionalArgs = {}> = (
      */
     skipValidation?: boolean;
     trx?: Knex.Transaction<any, any>;
+    /**
+     * Uses `DISTINCT ON`, which is a feature unique to PostgreSQL.
+     *
+     * Keeps only the first row of each set of rows where the given (set of) column(s) is unique.
+     * Note that the “first row” of each set is unpredictable unless `ORDER BY` is used to
+     * ensure that the desired row appears first. If ordering is used, there is an important
+     * constraint, because the first expression of `ORDER BY` must be present **somewhere** in
+     * `DISTINCT ON` expressions. But, not all expressions of `ORDER BY` need to be in `DISTINCT ON`.
+     */
+    distinct?: Array<keyof InstanceDataOf<F>>;
   } & AdditionalArgs
 ) => Promise<Array<InstanceDataOf<F>>>;
 
@@ -161,6 +171,7 @@ export const defineRawModel =
       orderBy,
       skipValidation = false,
       trx,
+      distinct,
     } = {}) => {
       const builder = trx ? masterTable().transacting(trx) : replicaTable();
       const query = builder.where(prepareCondition(where ?? {})).select('*');
@@ -180,6 +191,18 @@ export const defineRawModel =
         query.orderBy(orderBy);
       }
 
+      if (distinct && distinct.length >= 1) {
+        if (
+          (orderBy?.length ?? 0) >= 1 &&
+          orderBy?.at(0)?.column !== distinct.at(0)
+        ) {
+          throw new Error(
+            'SELECT DISTINCT ON expressions must match initial ORDER BY expression'
+          );
+        }
+        query.distinctOn(distinct);
+      }
+
       const res = await query;
 
       if (skipValidation) {