https://github.com/dfordivam/persistent-cdc

Change data capture for persistent
https://github.com/dfordivam/persistent-cdc

Last synced: 6 days ago
JSON representation

Change data capture for persistent

• Host: GitHub
• URL: https://github.com/dfordivam/persistent-cdc
• Owner: dfordivam
• License: bsd-3-clause
• Created: 2016-11-06T05:07:27.000Z (about 8 years ago)
• Default Branch: master
• Last Pushed: 2017-01-23T16:39:52.000Z (almost 8 years ago)
• Last Synced: 2024-12-23T11:13:11.461Z (11 days ago)
• Language: Haskell
• Size: 39.1 KB
• Stars: 2
• Watchers: 4
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

Awesome Lists containing this project

README

        
# Change data capture for persistent

Use this library to enable change data capture when using persistent.

Usage:

  1. Use the `share` provided by `Database.Persist.CDC.TH`.

  2. Use `updateWithCDC` or `replaceWithCDC` API in place of `update` and `replace` to capture changes.

The `share` API will create additional data for every entry

For example 

```haskell

share "User" [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistLowerCase|

  User

    username Text

    email Text

    password ByteString

  Wiki

    title Text

    overview Text Maybe

    content Text

  |]

```

This will create the following data types

```haskell

data User = User {

  userUsername  :: Text,

  userEmail     :: Text,

  userPassword  :: ByteString

}

data Wiki = Wiki {

  wikiTitle     :: Text,

  wikiOverview  :: Maybe Text,

  wikiContent   :: Text

}

data UserHistory = UserHistory {

  userHistoryEditAuthorId :: UserId,

  userHistoryUser         :: UserId,

  userHistoryTimeStamp    :: UTCTime,

  userHistoryUsername     :: Maybe Text,

  userHistoryEmail        :: Maybe Text,

  userHistoryPassword     :: Maybe ByteString

}

data WikiHistory = WikiHistory {

  wikiHistoryEditAuthorId :: UserId,

  wikiHistoryWiki         :: WikiId,

  wikiHistoryTimeStamp    :: UTCTime,

  wikiHistoryTitle        :: Maybe Text,

  wikiHistoryOverview     :: (Maybe Text, Bool),

  wikiHistoryContent      :: Maybe Text

}

```

For each data type specified, this API will create a related `History data type.

The fields in these data type are described below

  - The `EditAuthorId` field in the stores the identity of the `User` who did the update.

    The type of this has to be specified in the `share` API.

  - Next the id of original data is stored.

  - Timestamp is the time of creation of history object which is same as update time.

  - For every field in the original data a field is present in the history object.

    The type of this field has `Maybe`, which indicates whether that field got

    modified or not. If the field is modifed then the old value is stored in the

    history object.

    If the original data definition had `Maybe` attribute to a field then we create 

    a tuple of original data with Bool. The value of Bool determines whether there is 

    any change in the data.

    So if `wikiOverview` got modified from `Nothing` to `Just "overview"` then the

    history will contain `(Nothing, True)` and if there is no change it will have

    `(Nothing, False)`.

These APIs are available to modify the data and capture the change automatically 

in history objects.

```haskell

    updateWithCDC ::

           => Key (EditAuthorType backend) 

              -> Key record

              -> [Update record]

              -> ReaderT backend m ()

    replaceWithCDC ::

           => Key (EditAuthorType backend) 

              -> Key record

              -> record

              -> ReaderT backend m ()

```

Example yesod code to handle update

```haskell

-- postEditWikiR :: WikiId -> Handler Html

postEditWikiR wikiKey = do

    userKey <- getCurrentUser -- some API to get current user

                              -- maybeAuthId etc.

    updateWithCDC userKey wikiKey [WikiContent =. newContent]

    ...

```