Rust ORM for ScyllaDB and Apache Cassandra

Use monstrous tandem of scylla and charybdis for your next project

⚠️ This project is currently in an early stage of development. Feedback and contributions are welcomed!

Charybdis is a ORM layer on top of scylla_rust_driver focused on easy of use and performance

Breaking changes

As of 0.4.13 UDT fields must be in the same order as they are in the database. This is due to scylla driver limitation that does not support named bind values. Earlier versions would automatically order fields by name, but this is no longer the case as ORM could not work with exiting UDTs.

Usage considerations:

• Provide and expressive API for CRUD & Complex Query operations on model as a whole
• Provide easy way to work with subset of model fields by using automatically generated partial_<model>! macro
• Provide easy way to run complex queries by using automatically generated find_<model>! macro
• Automatic migration tool analyzes the project files and runs migrations according to differences between the model definition and database

Performance consideration:

• It uses prepared statements (shard/token aware) -> bind values
• It expects CachingSession as a session arg for operations
• Queries are macro generated str constants (no concatenation at runtime)
• By using find_<model>! macro we can run complex queries that are generated at compile time as &'static str
• Although it has expressive API it's thin layer on top of scylla_rust_driver, and it does not introduce any significant overhead

Table of Contents

• Charybdis Models
  • Define Tables
  • Define UDTs
  • Define Materialized Views
• Automatic migration with charybdis-migrate
• Basic Operations
  • Insert
  • Find
    • Find by primary key
    • Find by partition key
    • Find by primary key associated
    • Available find functions
    • Custom filtering
  • Update
  • Delete
    • Macro generated delete helpers
    • Custom delete queries
• Configuration Options
• Batch Operations
  • Chunked Batch Operations
  • Batch Configuration
• Partial Model
  • Considerations
  • As Native
• Callbacks
  • Implementation
  • Triggering Callbacks
• Collection
  • Generated Collection Queries
  • Generated Collection Methods
• Ignored fields
• Roadmap

Charybdis Models

Define Tables

use charybdis::macros::charybdis_model;
use charybdis::types::{Text, Timestamp, Uuid};

#[charybdis_model(
    table_name = users,
    partition_keys = [id],
    clustering_keys = [],
    global_secondary_indexes = [username],
    local_secondary_indexes = [],
    static_columns = []
)]
pub struct User {
    pub id: Uuid,
    pub username: Text,
    pub email: Text,
    pub created_at: Timestamp,
    pub updated_at: Timestamp,
    pub address: Address,
}

Define UDT

 use charybdis::macros::charybdis_udt_model;
 use charybdis::types::Text;
 
 #[charybdis_udt_model(type_name = address)]
 pub struct Address {
     pub street: Text,
     pub city: Text,
     pub state: Option<Text>,
     pub zip: Text,
     pub country: Text,
 }

🚨 UDT fields must be in the same order as they are in the database.

Note that in order for migration to correctly detect changes on each migration, type_name has to match struct name. So if we have struct ReorderData we have to use #[charybdis_udt_model(type_name = reorderdata)] - without underscores.

Define Materialized Views

use charybdis::macros::charybdis_view_model;
use charybdis::types::{Text, Timestamp, Uuid};

#[charybdis_view_model(
    table_name=users_by_username,
    base_table=users,
    partition_keys=[username],
    clustering_keys=[id]
)]
pub struct UsersByUsername {
    pub username: Text,
    pub id: Uuid,
    pub email: Text,
    pub created_at: Timestamp,
    pub updated_at: Timestamp,
}

Resulting auto-generated migration query will be:

CREATE MATERIALIZED VIEW IF NOT EXISTS users_by_email
AS SELECT created_at, updated_at, username, email, id
FROM users
WHERE email IS NOT NULL AND id IS NOT NULL
PRIMARY KEY (email, id)

Automatic migration

• charybdis-migrate enables automatic migration to database without need to write migrations by hand. It iterates over project files and generates migrations based on differences between model definitions and database. It supports following operations:

  • Create new tables
  • Create new columns
  • Drop columns
  • Change field types (drop and recreate column --drop-and-replace flag)
  • Create secondary indexes
  • Drop secondary indexes
  • Create UDTs
  • Create materialized views
  • Table options

      #[charybdis_model(
          table_name = commits,
          partition_keys = [object_id],
          clustering_keys = [created_at, id],
          global_secondary_indexes = [],
          local_secondary_indexes = [],
          table_options = #r"
              WITH CLUSTERING ORDER BY (created_at DESC) 
              AND gc_grace_seconds = 86400
          ";
      )]
      #[derive(Serialize, Deserialize, Default)]
      pub struct Commit {...}
    

    • ⚠️ If table exists, table options will result in alter table query that without CLUSTERING ORDER and COMPACT STORAGE options.

  Model dropping is not added. If you removed model, you need to drop table manuall

• Running migration

  cargo install charybdis-migrate
  
  migrate --hosts <host> --keyspace <your_keyspace> --drop-and-replace (optional)
  

  ⚠️ If you are working with existing datasets, before running migration you need to make sure that your **model ** definitions structure matches the database in respect to table names, column names, column types, partition keys, clustering keys and secondary indexes so you don't alter structure accidentally. If structure is matched, it will not run any migrations. As mentioned above, in case there is no model definition for table, it will not drop it. In future, we will add modelize command that will generate src/models files from existing data source.

• Global secondary indexes

  If we have model:

  #[charybdis_model(
      table_name = users,
      partition_keys = [id],
      clustering_keys = [],
      global_secondary_indexes = [username]
  )]
  

  resulting query will be: CREATE INDEX ON users (username);

• Local secondary Indexes

  Indexes that are scoped to the partition key

  #[charybdis_model(
      table_name = menus,
      partition_keys = [location],
      clustering_keys = [name, price, dish_type],
      global_secondary_indexes = [],
      local_secondary_indexes = [dish_type]
  )]
  

  resulting query will be: CREATE INDEX ON menus((location), dish_type);

Basic Operations:

For each operation you need to bring respective trait into scope. They are defined in charybdis::operations module.

Insert

• use charybdis::{CachingSession, Insert};
  
  #[tokio::main]
  async fn main() {
    let session: &CachingSession; // init sylla session
    
    // init user
    let user: User = User {
      id,
      email: "charybdis@nodecosmos.com".to_string(),
      username: "charybdis".to_string(),
      created_at: Utc::now(),
      updated_at: Utc::now(),
      address: Some(
          Address {
              street: "street".to_string(),
              state: "state".to_string(),
              zip: "zip".to_string(),
              country: "country".to_string(),
              city: "city".to_string(),
          }
      ),
    };
  
    // create
    user.insert().execute(&session).await;
  }
  

Find

• Find by primary key

    let user = User {id, ..Default::default()};
    let user = user.find_by_primary_key().execute(&session).await?;
  

• Find by partition key

    let users =  User {id, ..Default::default()}.find_by_partition_key().execute(&session).await;
  

• Find by primary key associated

  let users = User::find_by_primary_key_value(val: User::PrimaryKey).execute(&session).await;
  

• Available find functions

  use scylla::CachingSession;
  use charybdis::errors::CharybdisError;
  use charybdis::macros::charybdis_model;
  use charybdis::stream::CharybdisModelStream;
  use charybdis::types::{Date, Text, Uuid};
  
  #[charybdis_model(
      table_name = posts,
      partition_keys = [date],
      clustering_keys = [category_id, title],
      global_secondary_indexes = [category_id],
      local_secondary_indexes = [title]
  )]
  pub struct Post {
      pub date: Date,
      pub category_id: Uuid,
      pub title: Text,
  }
  
  impl Post {
      async fn find_various(db_session: &CachingSession) -> Result<(), CharybdisError> {
         let date = Date::default();
         let category_id = Uuid::new_v4();
         let title = Text::default();
      
         let posts: CharybdisModelStream<Post> = Post::find_by_date(date).execute(db_session).await?;
         let posts: CharybdisModelStream<Post> = Post::find_by_date_and_category_id(date, category_id).execute(db_session).await?;
         let posts: Post = Post::find_by_date_and_category_id_and_title(date, category_id, title.clone()).execute(db_session).await?;
      
         let post: Post = Post::find_first_by_date(date).execute(db_session).await?;
         let post: Post = Post::find_first_by_date_and_category_id(date, category_id).execute(db_session).await?;
      
         let post: Option<Post> = Post::maybe_find_first_by_date(date).execute(db_session).await?;
         let post: Option<Post> = Post::maybe_find_first_by_date_and_category_id(date, category_id).execute(db_session).await?;
         let post: Option<Post> = Post::maybe_find_first_by_date_and_category_id_and_title(date, category_id, title.clone()).execute(db_session).await?;
      
         // find by local secondary index
         let posts: CharybdisModelStream<Post> = Post::find_by_date_and_title(date, title.clone()).execute(db_session).await?;
         let post: Post = Post::find_first_by_date_and_title(date, title.clone()).execute(db_session).await?;
         let post: Option<Post> = Post::maybe_find_first_by_date_and_title(date, title.clone()).execute(db_session).await?;
  
        // find by global secondary index
        let posts: CharybdisModelStream<Post> = Post::find_by_category_id(category_id).execute(db_session).await?;
        let post: Post = Post::find_first_by_category_id(category_id).execute(db_session).await?;
        let post: Option<Post> = Post::maybe_find_first_by_category_id(category_id).execute(db_session).await?;
      
        Ok(())
      }
  }
  

• Custom filtering:

  Lets use our Post model as an example:

  #[charybdis_model(
      table_name = posts, 
      partition_keys = [category_id], 
      clustering_keys = [date, title],
      global_secondary_indexes = []
  )]
  pub struct Post {...}
  

  We get automatically generated find_post! macro that follows convention find_<struct_name>!. It can be used to create custom queries.

  Following will return stream of Post models, and query will be constructed at compile time as &'static str.

  // automatically generated macro rule
  let posts = find_post!("category_id in ? AND date > ?", (categor_vec, date))
      .execute(session)
      .await?;
  

  We can also use find_first_post! macro to get single result:

  let post = find_first_post!("category_id in ? AND date > ? LIMIT 1", (date, categor_vec))
      .execute(session)
      .await?;
  

  If we just need the Query and not the result, we can use find_post_query! macro:

  let query = find_post_query!("date = ? AND category_id in ?", (date, categor_vec));
  

Update

• let user = User::from_json(json);
  
  user.username = "scylla".to_string();
  user.email = "some@email.com";
  
  user.update().execute(&session).await;
  

• Collection:

  • Let's use our User model as an example:

    #[charybdis_model(
        table_name = users,
        partition_keys = [id],
        clustering_keys = [],
    )]
    pub struct User {
        id: Uuid,
        tags: Set<Text>,
        post_ids: List<Uuid>,
    }
    

  • push_to_<field_name> and pull_from_<field_name> methods are generated for each collection field.

    let user: User;
    
    user.push_tags(vec![tag]).execute(&session).await;
    user.pull_tags(vec![tag]).execute(&session).await;
    
    user.push_post_ids(vec![tag]).execute(&session).await;
    user.pull_post_ids(vec![tag]).execute(&session).await;
    

• Counter

  • Let's define post_counter model:

    #[charybdis_model(
        table_name = post_counters,
        partition_keys = [id],
        clustering_keys = [],
    )]
    pub struct PostCounter {
        id: Uuid,
        likes: Counter,
        comments: Counter,
    }
    

  • We can use increment_<field_name> and decrement_<field_name> methods to update counter fields.

    let post_counter: PostCounter;
    post_counter.increment_likes(1).execute(&session).await;
    post_counter.decrement_likes(1).execute(&session).await;
    
    post_counter.increment_comments(1).execute(&session).await;
    post_counter.decrement_comments(1).execute(&session).await;
    

Delete

• let user = User::from_json(json);
  
  user.delete().execute(&session).await;
  

• Macro generated delete helpers

  Lets use our Post model as an example:

  #[charybdis_model(
      table_name = posts,
      partition_keys = [date],
      clustering_keys = [categogry_id, title],
      global_secondary_indexes = [])
  ]
  pub struct Post {
      date: Date,
      category_id: Uuid,
      title: Text,
      id: Uuid,
      ...
  }
  

  We have macro generated functions for up to 3 fields from primary key.

  Post::delete_by_date(date: Date).execute(&session).await?;
  Post::delete_by_date_and_category_id(date: Date, category_id: Uuid).execute(&session).await?;
  Post::delete_by_date_and_category_id_and_title(date: Date, category_id: Uuid, title: Text).execute(&session).await?;
  

• Custom delete queries

  We can use delete_post! macro to create custom delete queries.

  delete_post!("date = ? AND category_id in ?", (date, category_vec)).execute(&session).await?
  

Configuration

Every operation returns CharybdisQuery that can be configured before execution with method chaining.

let user: User = User::find_by_id(id)
    .consistency(Consistency::One)
    .timeout(Some(Duration::from_secs(5)))
    .execute(&app.session)
    .await?;
    
let result: QueryResult = user.update().consistency(Consistency::One).execute(&session).await?;

Supported configuration options:

• consistency
• serial_consistency
• timestamp
• timeout
• page_size
• timestamp

Batch

CharybdisModelBatch operations are used to perform multiple operations in a single batch.

• Batch Operations

  let users: Vec<User>;
  let batch = User::batch();
  
  // inserts
  batch.append_inserts(users);
  
  // or updates
  batch.append_updates(users);
  
  // or deletes
  batch.append_deletes(users);
  
  batch.execute(&session).await?;
  

• Chunked Batch Operations

  Chunked batch operations are used to operate on large amount of data in chunks.

    let users: Vec<User>;
    let chunk_size = 100;
  
    User::batch().chunked_inserts(&session, users, chunk_size).await?;
    User::batch().chunked_updates(&session, users, chunk_size).await?;
    User::batch().chunked_deletes(&session, users, chunk_size).await?;
  

• Batch Configuration

  Batch operations can be configured before execution with method chaining.

  let batch = User::batch()
      .consistency(Consistency::One)
      .retry_policy(Some(Arc::new(DefaultRetryPolicy::new())))
      .chunked_inserts(&session, users, 100)
      .await?;
  

  We could also use method chaining to append operations to batch:

  let batch = User::batch()
      .consistency(Consistency::One)
      .retry_policy(Some(Arc::new(DefaultRetryPolicy::new())))
      .append_update(&user_1)
      .append_update(&user_2)
      .execute(data.db_session())
      .await?;
  

• Statements Batch

  We can use batch statements to perform collection operations in batch:

  let batch = User::batch();
  let users: Vec<User>;
  
  for user in users {
      batch.append_statement(User::PUSH_TAGS_QUERY, (vec![tag], user.id));
  }
  
  batch.execute(&session).await;
  

Partial Model:

• Use auto generated partial_<model>! macro to run operations on subset of the model fields. This macro generates a new struct with same structure as the original model, but only with provided fields. Macro is automatically generated by #[charybdis_model]. It follows convention partial_<struct_name>!.

  // auto-generated macro - available in crate::models::user
  partial_user!(UpdateUsernameUser, id, username);
  

  Now we have new struct UpdateUsernameUser that is equivalent to User model, but only with id and username fields.

  let mut update_user_username = UpdateUsernameUser {
      id,
      username: "updated_username".to_string(),
  };
  
  update_user_username.update().execute(&session).await?;
  

• Partial Model Considerations:

  1. partial_<model> requires #[derive(Default)] on original model
  2. partial_<model> require complete primary key in definition
  3. All derives that are defined bellow #charybdis_model macro will be automatically added to partial model.
  4. partial_<model> struct implements same field attributes as original model, so if we have #[serde(rename = "rootId")] on original model field, it will be present on partial model field.

• As Native

  In case we need to run operations on native model, we can use as_native method:

  let native_user: User = update_user_username.as_native().find_by_primary_key().execute(&session).await?;
  // action that requires native model
  authorize_user(&native_user);
  

  as_native works by returning new instance of native model with fields from partial model. For other fields it uses default values.

• Recommended naming convention is Purpose + Original Struct Name. E.g: UpdateAdresssUser, UpdateDescriptionPost.

Callbacks

Callbacks are convenient way to run additional logic on model before or after certain operations. E.g.

• we can use before_insert to set default values and/or validate model before insert.
• we can use after_update to update other data sources, e.g. elastic search.

Implementation:

1. Let's say we define custom extension that will be used to update elastic document on every post update:

   pub struct AppExtensions {
       pub elastic_client: ElasticClient,
   }
   

2. Now we can implement Callback that will utilize this extension:

   #[charybdis_model(...)]
   pub struct Post {}
   
   impl ExtCallbacks for Post {
       type Extention = AppExtensions;
       type Error = AppError; // From<CharybdisError>
       
      // use before_insert to set default values
       async fn before_insert(
           &mut self,
           _session: &CachingSession,
           extension: &AppExtensions,
       ) -> Result<(), CustomError> {
           self.id = Uuid::new_v4();
           self.created_at = Utc::now();
           
           Ok(())
       }
       
       // use before_update to set updated_at
       async fn before_update(
           &mut self,
           _session: &CachingSession,
           extension: &AppExtensions,
       ) -> Result<(), CustomError> {
           self.updated_at = Utc::now();
           
           Ok(())
       }
   
       // use after_update to update elastic document
       async fn after_update(
           &mut self,
           _session: &CachingSession,
           extension: &AppExtensions,
       ) -> Result<(), CustomError> {
           extension.elastic_client.update(...).await?;
   
           Ok(())
       }
       
       // use after_delete to delete elastic document
       async fn after_delete(
           &mut self,
           _session: &CachingSession,
           extension: &AppExtensions,
       ) -> Result<(), CustomError> {
           extension.elastic_client.delete(...).await?;
   
           Ok(())
       }
   }
   

• Possible Callbacks:

  • before_insert
  • before_update
  • before_delete
  • after_insert
  • after_update
  • after_delete

• Triggering Callbacks

  In order to trigger callback we use <operation>_cb. method: insert_cb, update_cb, delete_cb according traits. This enables us to have clear distinction between insert and insert with callbacks (insert_cb). Just as on main operation, we can configure callback operation query before execution.

   use charybdis::operations::{DeleteWithCallbacks, InsertWithCallbacks, UpdateWithCallbacks};
  
   post.insert_cb(app_extensions).execute(&session).await;
   post.update_cb(app_extensions).execute(&session).await;
   post.delete_cb(app_extensions).consistency(Consistency::All).execute(&session).await;
  

Collections

For each collection field, we get following:

• PUSH_<field_name>_QUERY static str
• PULL_<field_name>_QUERY static str
• push_<field_name> method
• pull_<field_name> method

1. Model:

   #[charybdis_model(
       table_name = users,
       partition_keys = [id],
       clustering_keys = []
   )]
   pub struct User {
       id: Uuid,
       tags: Set<Text>,
       post_ids: List<Uuid>,
       books_by_genre: Map<Text, Frozen<List<Text>>>,
   }
   

2. Generated Collection Queries:

   User::PUSH_TAGS_QUERY;
   User::PULL_TAGS_QUERY;
   
   User::PUSH_POST_IDS_QUERY;
   User::PULL_POST_IDS_QUERY;
   

   Generated query will expect value as first bind value and primary key fields as next bind values.

   impl User {
     const PUSH_TAGS_QUERY: &'static str = "UPDATE users SET tags = tags + ? WHERE id = ?";
     const PULL_TAGS_QUERY: &'static str = "UPDATE users SET tags = tags - ? WHERE id = ?";.
      
     const PUSH_POST_IDS_QUERY: &'static str = "UPDATE users SET post_ids = post_ids + ? WHERE id = ?";
     const PULL_POST_IDS_QUERY: &'static str = "UPDATE users SET post_ids = post_ids - ? WHERE id = ?";
   
     const PUSH_BOOKS_BY_GENRE_QUERY: &'static str = "UPDATE users SET books_by_genre = books_by_genre + ? WHERE id = ?";
     const PULL_BOOKS_BY_GENRE_QUERY: &'static str = "UPDATE users SET books_by_genre = books_by_genre - ? WHERE id = ?";
   }
   

   Now we could use this constant within Batch operations.

   let batch = User::batch();
   let users: Vec<User>;
   
   for user in users {
       batch.append_statement(User::PUSH_TAGS_QUERY, (vec![tag], user.id));
   }
   
   batch.execute(&session).await;
   

3. Generated Collection Methods:

   push_to_<field_name> and pull_from_<field_name> methods are generated for each collection field.

   let user: User::new();
   
   user.push_tags(tags: HashSet<T>).execute(&session).await;
   user.pull_tags(tags: HashSet<T>).execute(&session).await;
   
   
   user.push_post_ids(ids: Vec<T>).execute(&session).await;
   user.pull_post_ids(ids: Vec<T>).execute(&session).await;
   
   user.push_books_by_genre(map: HashMap<K, V>).execute(&session).await;
   user.pull_books_by_genre(map: HashMap<K, V>).execute(&session).await;
   

Ignored fields

We can ignore fields by using #[charybdis(ignore)] attribute:

#[charybdis_model(...)]
pub struct User {
    id: Uuid,
    #[charybdis(ignore)]
    organization: Option<Organization>,
}

So field organization will be ignored in all operations and default value will be used when deserializing from other data sources. It can be used to hold data that is not persisted in database.