ScyllaDb/Cassandra Object-Relation Mapper

Features

This library contains several crates with the following features:

• Automatic map tables to Rust structs: scylla_orm_table_to_struct. See Usage. See the generated dir for the generated code.
• Compile time checked queries: scylla_orm_macro (scylla_orm_macro::query). See Usage.
• Plugin derive macro to generate business logic: scylla_orm_macro (scylla_orm_macro::mirror)
• Automatic JSON mapping. When there is a column with type text, you can implement the Transformer trait and map it to a type that implements serde::Serialize and serde::Deserialize
• All queries are executed as a prepared statement
• Support for Materialized Views (and mapping between the base table if the columns are the same)

Not all types are supported yet due to https://github.com/scylladb/scylla-rust-driver/issues/104

Query types

Depending on a query, a certain query type can be derived. These can be found here. These are the commonly used query types:

• SelectMultiple: Can be used as an iterator to iterate over the rows
• SelectUnique: Selects an optional unique row by full primary key
• SelectUniqueExpect: Same as SelectUnique, but fails if the row doesn't exist
• SelectUniqueExpect with Count as entity type: has the special select_count method for queries like "select count(*) from ..."

There are also structs for CRUD operations.

Usage

Automatic map tables to Rust

You can see an example on how to generate Rust structs in the example dir.

• In the build.rs file the Transformer trait is implemented and used for json mapping
• In the generated dir you can see the generated structs

How to implement it yourself (step-by-step guide how to mimic the example crate):

• Add a build-dependency: scylla_orm_table_to_struct = "0.1"
• Create a build.rs file
• Optionally implement the Tranformer trait (or use DefaultTransformer)
• Call scylla_orm_table_to_struct::generate
• Build the project

An example of the structure of the generated code for table 'child' is:

• Child: a struct with owned values. Can be converted to ChildRef, PrimaryKey and PrimaryKeyRef
• ChildRef: a struct where the values are all borrowed. This struct can perform insertions. Can be converted to Child, PrimaryKey and PrimaryKeyRef
• PrimaryKey: a struct which holds the owned values of the primary key fields of Child. Can be converted to PrimaryKeyRef.
• PrimaryKeyRef: a struct where the values are all borrowed. This struct can perform updates, deletions and selects. Can be converted to PrimaryKey
• UpdatableColumn: an enum which holds the enum variants with owned values of columns that can be updated. Can be converted to UpdatableColumnRef.
• UpdatableColumnRef: an enum where the values are all borrowed. This is used by PrimaryKeyRef for updates. Can be converted to UpdatableColumn.

Macros

Crate scylla_orm_macro holds several macros that can be used to ensure compile/type checked queries. Examples on how this can be used can be found in lib.rs, method qmd.

How to implement it yourself:

• Add dependency: scylla_orm_macro = "0.1"
• The query macro returns the correct query type for the given query
• The query_base_table macro transforms a select query to the materialized view table, to a select query of the base table
• mirror and primary_key can be used for other derive macros