Fix duplicate derived collection items when modifying source collection (#116)

A derived collection is dependent on a collection field, e.g.
`trustsSearch-field-flow`. When a user adds a collection item, the
`sourceJson` for the derived collection contains a value with that key.
When a user modifies the collection item, an additional key is added to
the `sourceJson` (in the case of the example above,
`Data[trustsSearch-field-flow]`). This causes the item to be duplicated
in the returned list, so keys of this format need to be ignored.

Author: danlivings-dxw

src/DfE.ExternalApplications.Infrastructure/Services/DerivedCollectionFlowService.cs

@@ -211,7 +211,7 @@ private List<DerivedCollectionItem> ProcessCollectionSource(string sourceJson, D
                         foreach (var kvp in item)
                         {
                             // Skip metadata fields
-                            if (kvp.Key == "id" || kvp.Key == "_metadata") continue;
+                            if (kvp.Key == "id" || kvp.Key == "_metadata" || kvp.Key.StartsWith("Data[") || kvp.Key.StartsWith("Data_")) continue;
 
                             // Try to extract autocomplete data from the field value
                             if (kvp.Value != null)

src/Tests/DfE.ExternalApplications.Infrastructure.UnitTests/Services/DerivedCollectionFlowServiceTests.cs

@@ -62,4 +62,34 @@ public void GenerateItemsFromSourceField_for_collection_correctly_html_escapes_s
         Assert.Equal("some foo", item.DisplayName);
         Assert.Equal("Not signed yet", item.Status);
     }
+
+    [Theory]
+    [InlineData("[{\"foo\":\"{"id":"123456","name":"some foo"}\",\"bar\":123,\"Data[foo]\":\"{\\\"id\\\":\\\"456789\\\",\\\"name\\\":\\\"another foo\\\"}\"}]")]
+    [InlineData("[{\"foo\":\"{"id":"123456","name":"some foo"}\",\"bar\":123,\"Data_foo\":\"{\\\"id\\\":\\\"456789\\\",\\\"name\\\":\\\"another foo\\\"}\"}]")]
+    public void GenerateItemsFromSourceField_does_not_return_duplicate_entries_when_source_collection_is_modified(string sourceJson)
+    {
+        // A derived collection is dependent on a collection field, e.g. `trustsSearch-field-flow`.
+        // When a user adds a collection item, the `sourceJson` for the derived collection contains a value with that
+        // key.
+        // When a user modifies the collection item, an additional key is added to the `sourceJson` (in the case of the
+        // example above, `Data[trustsSearch-field-flow]` or `Data_trustsSearch-field-flow`).
+        // This causes the item to be duplicated in the returned list, so keys of these formats need to be ignored.
+        
+        var fieldId = _fixture.Create<string>();
+        var formData = new Dictionary<string, object>
+        {
+            [fieldId] = sourceJson,
+        };
+        var config = _fixture.Build<DerivedCollectionFlowConfiguration>()
+            .With(c => c.SourceType, "collection")
+            .Create();
+
+        var result = _service.GenerateItemsFromSourceField(fieldId, formData, config);
+        
+        Assert.NotEmpty(result);
+        var item = Assert.Single(result);
+        Assert.Equal("123456", item.Id);
+        Assert.Equal("some foo", item.DisplayName);
+        Assert.Equal("Not signed yet", item.Status);
+    }
 }