237069c827
- add jz_bm_materials.revision (default 1), read-only for GORM
- bump it only on content changes (models.ReviseMaterial)
- PUT /materials/{id} locks the row and answers 409 to a stale revision
- management answers carry revision and updated_at, the student detail
carries revision
115 lines
3.8 KiB
Go
115 lines
3.8 KiB
Go
package models
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import (
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"encoding/json"
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"slices"
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"strings"
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"gorm.io/gorm"
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)
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// A material's revision counts changes to its content only (D-03): the
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// title, type, body, source, url, course, zjazd (meeting) and tag set.
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// Visibility, shares, publication, the author and attached files never bump
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// it, so a writer holding an older revision is refused only when the note
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// itself changed since.
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// materialFingerprint is the content of a material that its revision
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// counts, in a fixed key order.
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type materialFingerprint struct {
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CourseID *uint `json:"course_id"`
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MeetingID *uint `json:"meeting_id"`
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Title string `json:"title"`
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Type string `json:"type"`
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Body *string `json:"body"`
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Source *string `json:"source"`
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URL *string `json:"url"`
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Tags []string `json:"tags"`
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}
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// MaterialFingerprint is the comparable form of m's content with the given
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// tag slugs: two materials with the same fingerprint have the same content
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// under D-03. Blank optional text counts as null, as BeforeSave stores it,
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// and the tag order does not matter. published_at, is_private, the author
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// and the shares are not inputs.
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func MaterialFingerprint(m Material, tagSlugs []string) string {
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body, source, url := m.Body, m.Source, m.URL
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blank(&body, &source, &url)
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tags := slices.Clone(tagSlugs)
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if tags == nil {
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tags = []string{}
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}
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slices.Sort(tags)
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raw, _ := json.Marshal(materialFingerprint{
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CourseID: m.CourseID,
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MeetingID: m.MeetingID,
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Title: m.Title,
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Type: m.Type,
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Body: body,
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Source: source,
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URL: url,
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Tags: tags,
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})
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return string(raw)
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}
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// materialState reads the content fingerprint and the revision of material
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// id through tx; a missing row is gorm.ErrRecordNotFound.
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func materialState(tx *gorm.DB, id uint) (string, uint, error) {
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db := tx.Session(&gorm.Session{NewDB: true})
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var m Material
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res := db.Select("id", "course_id", "meeting_id", "title", "type", "body", "source", "url", "revision").
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Where("id = ?", id).Limit(1).Find(&m)
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if res.Error != nil {
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return "", 0, res.Error
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}
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if res.RowsAffected == 0 {
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return "", 0, gorm.ErrRecordNotFound
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}
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var slugs []string
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err := db.Table(Tag{}.TableName()).
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Joins("JOIN "+MaterialTag{}.TableName()+" ON "+MaterialTag{}.TableName()+".tag_id = "+Tag{}.TableName()+".id").
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Where(MaterialTag{}.TableName()+".material_id = ?", id).
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Pluck(Tag{}.TableName()+".slug", &slugs).Error
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if err != nil {
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return "", 0, err
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}
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for i := range slugs {
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slugs[i] = strings.TrimSpace(slugs[i])
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}
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return MaterialFingerprint(m, slugs), m.Revision, nil
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}
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// MaterialContent reads the content fingerprint (MaterialFingerprint) of
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// material id and its tags through tx. A writer takes it before a write and
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// hands it to ReviseMaterial after; a missing row is gorm.ErrRecordNotFound.
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func MaterialContent(tx *gorm.DB, id uint) (string, error) {
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fp, _, err := materialState(tx, id)
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return fp, err
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}
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// ReviseMaterial bumps the revision of material id by one when its content
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// read through tx differs from before (a MaterialContent taken before the
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// write), and answers the revision the row has then and whether it went
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// up. Only content counts (D-03): a write that changed only visibility,
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// shares, publication or files, or that sent identical content, keeps the
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// revision. It is the only writer of the revision column, which GORM treats
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// as read-only.
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func ReviseMaterial(tx *gorm.DB, id uint, before string) (uint, bool, error) {
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after, current, err := materialState(tx, id)
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if err != nil {
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return 0, false, err
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}
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if after == before {
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return current, false, nil
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}
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var revision uint
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err = tx.Session(&gorm.Session{NewDB: true}).
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Raw("UPDATE jz_bm_materials SET revision = revision + 1 WHERE id = ? RETURNING revision", id).
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Scan(&revision).Error
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if err != nil {
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return 0, false, err
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}
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return revision, true, nil
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}
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