[Feature] Populate fragments for polymorphic relations

packages/core/database/lib/query/helpers/populate/apply.js

@@ -446,6 +446,11 @@ const morphToMany = async (input, ctx) => {
     .where({
       [joinColumn.name]: referencedValues,
       ...(joinTable.on || {}),
+      // If the populateValue contains an "on" property,
+      // only populate the types defined in it
+      ...('on' in populateValue
+        ? { [morphColumn.typeColumn.name]: Object.keys(populateValue.on) }
+        : {}),
     })
     .orderBy([joinColumn.name, 'order'])
     .execute({ mapResults: false });
@@ -470,6 +475,8 @@ const morphToMany = async (input, ctx) => {
   }, {});
 
   const map = {};
+  const { on, ...typePopulate } = populateValue;
+
   for (const type of Object.keys(idsByType)) {
     const ids = idsByType[type];
 
@@ -483,7 +490,7 @@ const morphToMany = async (input, ctx) => {
     const qb = db.entityManager.createQueryBuilder(type);
 
     const rows = await qb
-      .init(populateValue)
+      .init(on && type in on ? on[type] : typePopulate)
       .addSelect(`${qb.alias}.${idColumn.referencedColumn}`)
       .where({ [idColumn.referencedColumn]: ids })
       .execute({ mapResults: false });
@@ -540,6 +547,8 @@ const morphToOne = async (input, ctx) => {
   }, {});
 
   const map = {};
+  const { on, ...typePopulate } = populateValue;
+
   for (const type of Object.keys(idsByType)) {
     const ids = idsByType[type];
 
@@ -552,7 +561,7 @@ const morphToOne = async (input, ctx) => {
     const qb = db.entityManager.createQueryBuilder(type);
 
     const rows = await qb
-      .init(populateValue)
+      .init(on && type in on ? on[type] : typePopulate)
       .addSelect(`${qb.alias}.${idColumn.referencedColumn}`)
       .where({ [idColumn.referencedColumn]: ids })
       .execute({ mapResults: false });
@@ -579,7 +588,16 @@ const morphToOne = async (input, ctx) => {
 
 //  TODO: Omit limit & offset to avoid needing a query per result to avoid making too many queries
 const pickPopulateParams = (populate) => {
-  const fieldsToPick = ['select', 'count', 'where', 'populate', 'orderBy', 'filters', 'ordering'];
+  const fieldsToPick = [
+    'select',
+    'count',
+    'where',
+    'populate',
+    'orderBy',
+    'filters',
+    'ordering',
+    'on',
+  ];
 
   if (populate.count !== true) {
     fieldsToPick.push('limit', 'offset');

packages/core/utils/lib/convert-query-params.js

@@ -6,17 +6,18 @@
  * Converts the standard Strapi REST query params to a more usable format for querying
  * You can read more here: https://docs.strapi.io/developer-docs/latest/developer-resources/database-apis-reference/rest-api.html#filters
  */
+
 const {
+  isNil,
+  toNumber,
+  isInteger,
   has,
   isEmpty,
   isObject,
   isPlainObject,
   cloneDeep,
   get,
   mergeAll,
-  isNil,
-  toNumber,
-  isInteger,
 } = require('lodash/fp');
 const _ = require('lodash');
 const parseType = require('./parse-type');
@@ -185,8 +186,23 @@ const convertPopulateObject = (populate, schema) => {
       return acc;
     }
 
-    // FIXME: This is a temporary solution for dynamic zones that should be
-    // fixed when we'll implement a more accurate way to query them
+    if (typeof subPopulate === 'object' && 'on' in subPopulate) {
+      return {
+        ...acc,
+        [key]: {
+          on: Object.entries(subPopulate.on).reduce(
+            (acc, [type, typeSubPopulate]) => ({
+              ...acc,
+              [type]: convertNestedPopulate(typeSubPopulate, strapi.getModel(type)),
+            }),
+            {}
+          ),
+        },
+      };
+    }
+
+    // TODO: Deprecated way of handling dynamic zone populate queries. It's kept as is,
+    // as removing it could break existing user queries but should be removed in V5.
     if (attribute.type === 'dynamiczone') {
       const populates = attribute.components
         .map((uid) => strapi.getModel(uid))