feat: zjazd (meeting) on readings and materials

The Pulpit hero lists what to read for the current or next zjazd, so
readings and materials get a nullable meeting_id (FK to jz_bm_meetings,
ON DELETE SET NULL, indexed). The reading admin form gets a "Na zjazd"
picker, the student reading JSON carries meeting_id, and the management
/readings records filter and validate it.

controllers/api/json.go

@@ -173,6 +173,7 @@ type readingJSON struct {
 	ID         uint       `json:"id"`
 	CourseID   uint       `json:"course_id"`
 	Course     *courseRef `json:"course"`
+	MeetingID  *uint      `json:"meeting_id"`
 	Title      string     `json:"title"`
 	Author     *string    `json:"author"`
 	Source     *string    `json:"source"`

controllers/api/json_test.go

@@ -0,0 +1,28 @@
+package api
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+)
+
+// TestReadingJSONCarriesMeetingID checks that meeting_id is always present
+// in a reading, as a number or as null.
+func TestReadingJSONCarriesMeetingID(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(readingJSON{ID: 1, Title: "Lektura", MeetingID: tc.meeting})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !strings.Contains(string(b), tc.want) {
+			t.Errorf("reading JSON %s does not contain %s", b, tc.want)
+		}
+	}
+}

controllers/api/readings.go

@@ -42,6 +42,7 @@ func listReadings(db *gorm.DB, userID, courseID uint) ([]readingJSON, error) {
 			ID:         row.ID,
 			CourseID:   idOf(row.CourseID),
 			Course:     newCourseRef(courses[idOf(row.CourseID)]),
+			MeetingID:  row.MeetingID,
 			Title:      row.Title,
 			Author:     row.Author,
 			Source:     row.Source,