Add databaseId to assignees GraphQL fragment

The assignees query fragment only requested id, login, and name but the
GitHubUser struct includes a DatabaseID field. Since the field was never
requested from the API, it always defaulted to Go's zero value (0) in
JSON output. This adds databaseId to the fragment so the actual value is
returned.

Also adds ExportData test cases for assignees on both Issue and
PullRequest to verify databaseId round-trips correctly through JSON
serialization.

api/export_pr_test.go

@@ -107,6 +107,32 @@ func TestIssue_ExportData(t *testing.T) {
 				}
 			`),
 		},
+		{
+			name:   "assignees",
+			fields: []string{"assignees"},
+			inputJSON: heredoc.Doc(`
+				{ "assignees": { "nodes": [
+					{
+						"id": "MDQ6VXNlcjE=",
+						"login": "monalisa",
+						"name": "Mona Lisa",
+						"databaseId": 1234
+					}
+				] } }
+			`),
+			outputJSON: heredoc.Doc(`
+				{
+					"assignees": [
+						{
+							"id": "MDQ6VXNlcjE=",
+							"login": "monalisa",
+							"name": "Mona Lisa",
+							"databaseId": 1234
+						}
+					]
+				}
+			`),
+		},
 		{
 			name:   "linked pull requests",
 			fields: []string{"closedByPullRequestsReferences"},
@@ -316,6 +342,32 @@ func TestPullRequest_ExportData(t *testing.T) {
 				}
 			`),
 		},
+		{
+			name:   "assignees",
+			fields: []string{"assignees"},
+			inputJSON: heredoc.Doc(`
+				{ "assignees": { "nodes": [
+					{
+						"id": "MDQ6VXNlcjE=",
+						"login": "monalisa",
+						"name": "Mona Lisa",
+						"databaseId": 1234
+					}
+				] } }
+			`),
+			outputJSON: heredoc.Doc(`
+				{
+					"assignees": [
+						{
+							"id": "MDQ6VXNlcjE=",
+							"login": "monalisa",
+							"name": "Mona Lisa",
+							"databaseId": 1234
+						}
+					]
+				}
+			`),
+		},
 		{
 			name:   "linked issues",
 			fields: []string{"closingIssuesReferences"},

api/query_builder.go

@@ -388,7 +388,7 @@ func IssueGraphQL(fields []string) string {
 		case "headRepository":
 			q = append(q, `headRepository{id,name}`)
 		case "assignees":
-			q = append(q, `assignees(first:100){nodes{id,login,name},totalCount}`)
+			q = append(q, `assignees(first:100){nodes{id,login,name,databaseId},totalCount}`)
 		case "assignedActors":
 			q = append(q, assignedActors)
 		case "labels":

api/query_builder_test.go

@@ -21,7 +21,7 @@ func TestPullRequestGraphQL(t *testing.T) {
 		{
 			name:   "fields with nested structures",
 			fields: []string{"author", "assignees"},
-			want:   "author{login,...on User{id,name}},assignees(first:100){nodes{id,login,name},totalCount}",
+			want:   "author{login,...on User{id,name}},assignees(first:100){nodes{id,login,name,databaseId},totalCount}",
 		},
 		{
 			name:   "compressed query",
@@ -67,7 +67,7 @@ func TestIssueGraphQL(t *testing.T) {
 		{
 			name:   "fields with nested structures",
 			fields: []string{"author", "assignees"},
-			want:   "author{login,...on User{id,name}},assignees(first:100){nodes{id,login,name},totalCount}",
+			want:   "author{login,...on User{id,name}},assignees(first:100){nodes{id,login,name,databaseId},totalCount}",
 		},
 		{
 			name:   "compressed query",