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fix: entity null fetch produces resolver error #1379

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Merged
dkorittki merged 14 commits into from
Apr 9, 2026
+339 −0
Merged

fix: entity null fetch produces resolver error #1379

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2e45538
fix: don't treat subgraph entity null responses as errors
dkorittki Feb 9, 2026
9ad08ba
chore: add comments for context
dkorittki Feb 10, 2026
386c9bc
chore: add test for nullable fields + fix test assumption
dkorittki Feb 10, 2026
afa8127
chore: fix test
dkorittki Feb 10, 2026
ef3c27e
fix: use gomock.Any in test method call assumption
dkorittki Feb 10, 2026
2715b7a
fix: use new func signature in tests
dkorittki Feb 10, 2026
25e1453
Merge branch 'master' into dominik/eng-7492-fix-data-entities-null-pr…
dkorittki Feb 20, 2026
540c6fb
chore: deduce data path from fetch kind
dkorittki Feb 20, 2026
90eee4a
chore: add null batch entity test
dkorittki Feb 20, 2026
2df3968
chore: add test to verify null data behaviour
dkorittki Feb 20, 2026
8542fe4
Merge branch 'master' into dominik/eng-7492-fix-data-entities-null-pr…
dkorittki Feb 23, 2026
383faee
Merge branch 'master' into dominik/eng-7492-fix-data-entities-null-pr…
dkorittki Mar 2, 2026
782b2c3
Merge branch 'master' into dominik/eng-7492-fix-data-entities-null-pr…
dkorittki Apr 9, 2026
29ee2f0
chore: add test to verify errors are propagated on null entities
dkorittki Apr 9, 2026
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21 changes: 21 additions & 0 deletions v2/pkg/engine/resolve/loader.go
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Original file line number Diff line number Diff line change
Expand Up @@ -538,6 +538,12 @@ func (l *Loader) mergeResult(fetchItem *FetchItem, res *result, items []*astjson

// Check if data needs processing.
if res.postProcessing.SelectResponseDataPath != nil && astjson.ValueIsNull(responseData) {
// First check if this is actually an entity null fetch, instead of a data null fetch.
// In this case we return early to avoid adding subgraph errors or merging this into items.
if isEmptyEntityFetch(fetchItem, response) {
return nil
}

// When:
// - No errors or data are present
// - Status code is not within the 2XX range
Expand Down Expand Up @@ -633,6 +639,21 @@ func (l *Loader) mergeResult(fetchItem *FetchItem, res *result, items []*astjson
return nil
}

// isEmptyEntityFetch returns true if fetchItem resembles an sucessful entity fetch
// where no entity has been returned, else false.
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func isEmptyEntityFetch(fetchItem *FetchItem, response *astjson.Value) bool {
kind := fetchItem.Fetch.FetchKind()

if kind == FetchKindEntity || kind == FetchKindEntityBatch {
entitiesData := response.Get("data", "_entities")
if astjson.ValueIsNonNull(entitiesData) && entitiesData.Type() == astjson.TypeArray {
return true
}
}

return false
}

var (
errorsInvalidInputHeader = []byte(`{"errors":[{"message":"Failed to render Fetch Input","path":[`)
errorsInvalidInputFooter = []byte(`]}]}`)
Expand Down
318 changes: 318 additions & 0 deletions v2/pkg/engine/resolve/resolve_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2286,6 +2286,324 @@ func TestResolver_ResolveGraphQLResponse(t *testing.T) {
},
}, *NewContext(context.Background()), `{"errors":[{"message":"Failed to fetch from Subgraph 'Users' at Path 'query'."}],"data":null}`
}))
t.Run("fetch with null entity and non-nullable root field", testFn(func(t *testing.T, ctrl *gomock.Controller) (node *GraphQLResponse, ctx Context, expectedOutput string) {
mockDataSource := NewMockDataSource(ctrl)
mockDataSource.EXPECT().
Load(gomock.Any(), gomock.Any(), gomock.Any()).
DoAndReturn(func(ctx context.Context, headers http.Header, input []byte) ([]byte, error) {
// Subgraph returns null for the entity
return []byte(`{"data":{"_entities":[null]}}`), nil
})
return &GraphQLResponse{
Fetches: SingleWithPath(&EntityFetch{
Input: EntityInput{
Header: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`{"method":"POST","url":"http://users","body":{"query":"query($representations: [_Any!]!){_entities(representations: $representations){... on User {name}}}","variables":{"representations":[`),
SegmentType: StaticSegmentType,
},
},
},
Item: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`{"__typename":"User","id":"1"}`),
SegmentType: StaticSegmentType,
},
},
},
SkipErrItem: true,
Footer: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`]}}}`),
SegmentType: StaticSegmentType,
},
},
},
},
DataSource: mockDataSource,
PostProcessing: PostProcessingConfiguration{
SelectResponseDataPath: []string{"data", "_entities", "0"},
SelectResponseErrorsPath: []string{"errors"},
},
Info: &FetchInfo{
DataSourceID: "Users",
DataSourceName: "Users",
},
}, "query"),
Data: &Object{
Nullable: false,
Fields: []*Field{
{
Name: []byte("name"),
Value: &String{
Path: []string{"name"},
Nullable: false,
},
},
},
},
}, *NewContext(context.Background()), `{"errors":[{"message":"Cannot return null for non-nullable field 'Query.name'.","path":["name"]}],"data":null}`
}))
t.Run("fetch with null entity and nullable root field", testFn(func(t *testing.T, ctrl *gomock.Controller) (node *GraphQLResponse, ctx Context, expectedOutput string) {
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mockDataSource := NewMockDataSource(ctrl)
mockDataSource.EXPECT().
Load(gomock.Any(), gomock.Any(), gomock.Any()).
DoAndReturn(func(ctx context.Context, headers http.Header, input []byte) ([]byte, error) {
// Subgraph returns null for the entity
return []byte(`{"data":{"_entities":[null]}}`), nil
})
return &GraphQLResponse{
Fetches: SingleWithPath(&EntityFetch{
Input: EntityInput{
Header: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`{"method":"POST","url":"http://users","body":{"query":"query($representations: [_Any!]!){_entities(representations: $representations){... on User {name}}}","variables":{"representations":[`),
SegmentType: StaticSegmentType,
},
},
},
Item: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`{"__typename":"User","id":"1"}`),
SegmentType: StaticSegmentType,
},
},
},
SkipErrItem: true,
Footer: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`]}}}`),
SegmentType: StaticSegmentType,
},
},
},
},
DataSource: mockDataSource,
PostProcessing: PostProcessingConfiguration{
SelectResponseDataPath: []string{"data", "_entities", "0"},
SelectResponseErrorsPath: []string{"errors"},
},
Info: &FetchInfo{
DataSourceID: "Users",
DataSourceName: "Users",
},
}, "query"),
Data: &Object{
Nullable: false,
Fields: []*Field{
{
Name: []byte("name"),
Value: &String{
Path: []string{"name"},
Nullable: true,
},
},
},
},
}, *NewContext(context.Background()), `{"data":{"name":null}}`
}))
t.Run("fetch with null entity batch and non-nullable root field", testFn(func(t *testing.T, ctrl *gomock.Controller) (node *GraphQLResponse, ctx Context, expectedOutput string) {
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mockDataSource := NewMockDataSource(ctrl)
mockDataSource.EXPECT().
Load(gomock.Any(), gomock.Any(), gomock.Any()).
DoAndReturn(func(ctx context.Context, headers http.Header, input []byte) ([]byte, error) {
// Subgraph returns null for the entity
return []byte(`{"data":{"_entities":[null]}}`), nil
})
return &GraphQLResponse{
Fetches: SingleWithPath(&BatchEntityFetch{
Input: BatchInput{
Header: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`{"method":"POST","url":"http://users","body":{"query":"query($representations: [_Any!]!){_entities(representations: $representations){... on User {name}}}","variables":{"representations":[`),
SegmentType: StaticSegmentType,
},
},
},
Items: []InputTemplate{
{
Segments: []TemplateSegment{
{
Data: []byte(`{"__typename":"User","id":"1"}`),
SegmentType: StaticSegmentType,
},
},
},
},
SkipNullItems: true,
SkipErrItems: true,
Separator: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`,`),
SegmentType: StaticSegmentType,
},
},
},
Footer: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`]}}}`),
SegmentType: StaticSegmentType,
},
},
},
},
DataSource: mockDataSource,
PostProcessing: PostProcessingConfiguration{
SelectResponseDataPath: []string{"data", "_entities"},
SelectResponseErrorsPath: []string{"errors"},
},
Info: &FetchInfo{
DataSourceID: "Users",
DataSourceName: "Users",
},
}, "query"),
Data: &Object{
Nullable: false,
Fields: []*Field{
{
Name: []byte("name"),
Value: &String{
Path: []string{"name"},
Nullable: false,
},
},
},
},
}, *NewContext(context.Background()), `{"errors":[{"message":"Cannot return null for non-nullable field 'Query.name'.","path":["name"]}],"data":null}`
}))
t.Run("entity fetch with null data field in subgraph response", testFn(func(t *testing.T, ctrl *gomock.Controller) (node *GraphQLResponse, ctx Context, expectedOutput string) {
mockDataSource := NewMockDataSource(ctrl)
mockDataSource.EXPECT().
Load(gomock.Any(), gomock.Any(), gomock.Any()).
DoAndReturn(func(ctx context.Context, headers http.Header, input []byte) ([]byte, error) {
// Subgraph returns null for the data field itself (not an _entities array)
return []byte(`{"data":null}`), nil
})
return &GraphQLResponse{
Fetches: SingleWithPath(&EntityFetch{
Input: EntityInput{
Header: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`{"method":"POST","url":"http://users","body":{"query":"query($representations: [_Any!]!){_entities(representations: $representations){... on User {name}}}","variables":{"representations":[`),
SegmentType: StaticSegmentType,
},
},
},
Item: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`{"__typename":"User","id":"1"}`),
SegmentType: StaticSegmentType,
},
},
},
SkipErrItem: true,
Footer: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`]}}}`),
SegmentType: StaticSegmentType,
},
},
},
},
DataSource: mockDataSource,
PostProcessing: PostProcessingConfiguration{
SelectResponseDataPath: []string{"data", "_entities", "0"},
SelectResponseErrorsPath: []string{"errors"},
},
Info: &FetchInfo{
DataSourceID: "Users",
DataSourceName: "Users",
},
}, "query"),
Data: &Object{
Nullable: false,
Fields: []*Field{
{
Name: []byte("name"),
Value: &String{
Path: []string{"name"},
Nullable: true,
},
},
},
},
}, *NewContext(context.Background()), `{"errors":[{"message":"Failed to fetch from Subgraph 'Users' at Path 'query', Reason: no data or errors in response."}],"data":{"name":null}}`
}))
t.Run("entity fetch with null entity and error in subgraph response", testFn(func(t *testing.T, ctrl *gomock.Controller) (node *GraphQLResponse, ctx Context, expectedOutput string) {
// validates that when a subgraph returns {"data":{"_entities":[null]},"errors":[{"message":"errorMessage"}]}, the error is still propagated correctly

mockDataSource := NewMockDataSource(ctrl)
mockDataSource.EXPECT().
Load(gomock.Any(), gomock.Any(), gomock.Any()).
DoAndReturn(func(ctx context.Context, headers http.Header, input []byte) ([]byte, error) {
// Subgraph returns null for the entity but also includes an error
return []byte(`{"data":{"_entities":[null]},"errors":[{"message":"errorMessage"}]}`), nil
})
return &GraphQLResponse{
Fetches: SingleWithPath(&EntityFetch{
Input: EntityInput{
Header: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`{"method":"POST","url":"http://users","body":{"query":"query($representations: [_Any!]!){_entities(representations: $representations){... on User {name}}}","variables":{"representations":[`),
SegmentType: StaticSegmentType,
},
},
},
Item: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`{"__typename":"User","id":"1"}`),
SegmentType: StaticSegmentType,
},
},
},
SkipErrItem: true,
Footer: InputTemplate{
Segments: []TemplateSegment{
{
Data: []byte(`]}}}`),
SegmentType: StaticSegmentType,
},
},
},
},
DataSource: mockDataSource,
PostProcessing: PostProcessingConfiguration{
SelectResponseDataPath: []string{"data", "_entities", "0"},
SelectResponseErrorsPath: []string{"errors"},
},
Info: &FetchInfo{
DataSourceID: "Users",
DataSourceName: "Users",
},
}, "query"),
Data: &Object{
Nullable: false,
Fields: []*Field{
{
Name: []byte("name"),
Value: &String{
Path: []string{"name"},
Nullable: true,
},
},
},
},
}, *NewContext(context.Background()), `{"errors":[{"message":"Failed to fetch from Subgraph 'Users' at Path 'query'.","extensions":{"errors":[{"message":"errorMessage"}]}}],"data":{"name":null}}`
}))
t.Run("root field with nested non-nullable fields returns null", testFn(func(t *testing.T, ctrl *gomock.Controller) (node *GraphQLResponse, ctx Context, expectedOutput string) {
return &GraphQLResponse{
Fetches: Single(&SingleFetch{
Expand Down
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