Merge branch '312-having-many-link-row-fields-causes-the-tool-to-slow-down' into 'develop'

Resolve "Having many link row fields causes the backend to slow down"

Closes #312

See merge request bramw/baserow!174

backend/src/baserow/contrib/database/api/fields/serializers.py

@@ -1,5 +1,4 @@
 from django.utils.functional import lazy
-from django.db import models
 
 from drf_spectacular.utils import extend_schema_field
 from drf_spectacular.types import OpenApiTypes
@@ -66,21 +65,6 @@ class UpdateFieldSerializer(serializers.ModelSerializer):
         }
 
 
-class LinkRowListSerializer(serializers.ListSerializer):
-    def to_representation(self, data):
-        """
-        Data that is fetched is always from another Table model and when fetching
-        that data we always need to respect the field enhancements. Otherwise it
-        could for example fail when we want to fetch the related select options that
-        could be in another database and table.
-        """
-
-        if isinstance(data, models.Manager):
-            data = data.all().enhance_by_fields()
-
-        return super().to_representation(data)
-
-
 class LinkRowValueSerializer(serializers.Serializer):
     id = serializers.IntegerField(help_text='The unique identifier of the row in the '
                                             'related table.')

backend/src/baserow/contrib/database/fields/field_types.py

@@ -17,8 +17,8 @@ from rest_framework import serializers
 from baserow.core.models import UserFile
 from baserow.core.user_files.exceptions import UserFileDoesNotExist
 from baserow.contrib.database.api.fields.serializers import (
-    LinkRowListSerializer, LinkRowValueSerializer, FileFieldRequestSerializer,
-    FileFieldResponseSerializer, SelectOptionSerializer
+    LinkRowValueSerializer, FileFieldRequestSerializer, FileFieldResponseSerializer,
+    SelectOptionSerializer
 )
 from baserow.contrib.database.api.fields.errors import (
     ERROR_LINK_ROW_TABLE_NOT_IN_SAME_DATABASE, ERROR_LINK_ROW_TABLE_NOT_PROVIDED,
@@ -314,10 +314,35 @@ class LinkRowFieldType(FieldType):
 
     def enhance_queryset(self, queryset, field, name):
         """
-        Makes sure that the related rows are prefetched by Django.
+        Makes sure that the related rows are prefetched by Django. We also want to
+        enhance the primary field of the related queryset. If for example the primary
+        field is a single select field then the dropdown options need to be
+        prefetched in order to prevent many queries.
         """
 
-        return queryset.prefetch_related(name)
+        remote_model = queryset.model._meta.get_field(name).remote_field.model
+        related_queryset = remote_model.objects.all()
+
+        try:
+            primary_field_object = next(
+                object
+                for object in remote_model._field_objects.values()
+                if object['field'].primary
+            )
+            related_queryset = primary_field_object['type'].enhance_queryset(
+                related_queryset,
+                primary_field_object['field'],
+                primary_field_object['name']
+            )
+        except StopIteration:
+            # If the related model does not have a primary field then we also don't
+            # need to enhance the queryset.
+            pass
+
+        return queryset.prefetch_related(models.Prefetch(
+            name,
+            queryset=related_queryset
+        ))
 
     def get_serializer_field(self, instance, **kwargs):
         """
@@ -331,9 +356,9 @@ class LinkRowFieldType(FieldType):
     def get_response_serializer_field(self, instance, **kwargs):
         """
         If a model has already been generated it will be added as a property to the
-        instance. If that case then we can extract the primary field from the model and
-        we can pass the name along to the LinkRowValueSerializer. It will be used to
-        include the primary field's value in the response as a string.
+        instance. If that is the case then we can extract the primary field from the
+        model and we can pass the name along to the LinkRowValueSerializer. It will
+        be used to include the primary field's value in the response as a string.
         """
 
         primary_field_name = None
@@ -348,7 +373,7 @@ class LinkRowFieldType(FieldType):
             if primary_field:
                 primary_field_name = primary_field['name']
 
-        return LinkRowListSerializer(child=LinkRowValueSerializer(
+        return serializers.ListSerializer(child=LinkRowValueSerializer(
             value_field_name=primary_field_name, required=False, **kwargs
         ))
 

backend/tests/baserow/contrib/database/field/test_single_select_field_type.py

@@ -12,6 +12,9 @@ from baserow.contrib.database.fields.models import SelectOption, SingleSelectFie
 from baserow.contrib.database.fields.field_types import SingleSelectFieldType
 from baserow.contrib.database.rows.handler import RowHandler
 from baserow.contrib.database.views.handler import ViewHandler
+from baserow.contrib.database.api.rows.serializers import (
+    get_row_serializer_class, RowSerializer
+)
 
 
 @pytest.mark.django_db
@@ -502,7 +505,11 @@ def test_single_select_field_type_get_order(data_fixture):
 
 
 @pytest.mark.django_db
-def test_primary_single_select_field_with_link_row_field(api_client, data_fixture):
+def test_primary_single_select_field_with_link_row_field(
+    api_client,
+    data_fixture,
+    django_assert_num_queries
+):
     """
     We expect the relation to a table that has a single select field to work.
     """
@@ -528,7 +535,8 @@ def test_primary_single_select_field_with_link_row_field(api_client, data_fixtur
         type_name='single_select',
         select_options=[
             {'value': 'Option 1', 'color': 'red'},
-            {'value': 'Option 2', 'color': 'blue'}
+            {'value': 'Option 2', 'color': 'blue'},
+            {'value': 'Option 3', 'color': 'orange'}
         ],
         primary=True
     )
@@ -548,6 +556,10 @@ def test_primary_single_select_field_with_link_row_field(api_client, data_fixtur
         user=user, table=customers_table,
         values={f'field_{customers_primary.id}': select_options[1].id}
     )
+    customers_row_3 = row_handler.create_row(
+        user=user, table=customers_table,
+        values={f'field_{customers_primary.id}': select_options[2].id}
+    )
     row_handler.create_row(
         user, table=example_table,
         values={f'field_{link_row_field.id}': [customers_row_1.id, customers_row_2.id]}
@@ -556,6 +568,18 @@ def test_primary_single_select_field_with_link_row_field(api_client, data_fixtur
         user, table=example_table,
         values={f'field_{link_row_field.id}': [customers_row_1.id]}
     )
+    row_handler.create_row(
+        user, table=example_table,
+        values={f'field_{link_row_field.id}': [customers_row_3.id]}
+    )
+
+    model = example_table.get_model()
+    queryset = model.objects.all().enhance_by_fields()
+    serializer_class = get_row_serializer_class(model, RowSerializer, is_response=True)
+
+    with django_assert_num_queries(3):
+        serializer = serializer_class(queryset, many=True)
+        serializer.data
 
     response = api_client.get(
         reverse('api:database:rows:list', kwargs={'table_id': example_table.id}),
@@ -576,6 +600,10 @@ def test_primary_single_select_field_with_link_row_field(api_client, data_fixtur
         response_json['results'][1][f'field_{link_row_field.id}'][0]['value'] ==
         'Option 1'
     )
+    assert (
+        response_json['results'][2][f'field_{link_row_field.id}'][0]['value'] ==
+        'Option 3'
+    )
 
 
 @pytest.mark.django_db

changelog.md

@@ -21,6 +21,7 @@
 * Made it possible to configure SMTP settings via environment variables.
 * Added field name to the public REST API docs.
 * Made the public REST API docs compatible with smaller screens.
+* Reduced the amount of queries when using the link row field.
 
 ## Released (2021-02-04)
 

web-frontend/modules/database/fieldTypes.js

@@ -162,7 +162,7 @@ export class FieldType extends Registerable {
    * converted to string.
    */
   toHumanReadableString(field, value) {
-    return value
+    return value || ''
   }
 
   /**

web-frontend/modules/database/mixins/linkRowField.js

@@ -32,7 +32,7 @@ export default {
         .toHumanReadableString(primary, row[`field_${primary.id}`])
       newValue.push({
         id: row.id,
-        value: rowValue.toString(),
+        value: rowValue,
       })
       this.$emit('update', newValue, value)
     },