feat: materials by zjazd in the student API and admin

The material admin form gets the "Na zjazd" picker, every student
material JSON carries meeting_id, and GET /materials accepts meeting=
inside the published-only scope, so the Pulpit hero can list the
zjazd's materials next to its readings.

controllers/api/json_test.go

@@ -4,6 +4,8 @@ import (
 	"encoding/json"
 	"strings"
 	"testing"
+
+	"git.golem15.com/jakub/sm-bm-plugin/models"
 )
 
 // TestReadingJSONCarriesMeetingID checks that meeting_id is always present
@@ -26,3 +28,24 @@ func TestReadingJSONCarriesMeetingID(t *testing.T) {
 		}
 	}
 }
+
+// TestMaterialJSONCarriesMeetingID checks that meeting_id is always present
+// in a material, as a number or as null.
+func TestMaterialJSONCarriesMeetingID(t *testing.T) {
+	id := uint(4)
+	for _, tc := range []struct {
+		meeting *uint
+		want    string
+	}{
+		{&id, `"meeting_id":4`},
+		{nil, `"meeting_id":null`},
+	} {
+		b, err := json.Marshal(newMaterialListJSON(models.Material{ID: 1, Title: "Materiał", Type: "pdf", MeetingID: tc.meeting}, 0))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !strings.Contains(string(b), tc.want) {
+			t.Errorf("material JSON %s does not contain %s", b, tc.want)
+		}
+	}
+}