# entity-rs: Library & macros for entity data structures
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[![entity: rustc 1.49+]][Rust 1.49]
[![entity_macros: rustc 1.49+]][Rust 1.49]
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[Rust 1.49]: https://blog.rust-lang.org/2020/12/31/Rust-1.49.0.html
A simplistic framework based on [TAO, Facebook's distributed database for Social Graph](https://www.usenix.org/system/files/conference/atc13/atc13-bronson.pdf).
Requires Rust 1.49+.
## Getting Started
### Installation
Import **Entity** into your project by adding the following line to your
Cargo.toml. `entity_macros` contains the macros needed to derive and/or
transform your data to be compatible with supported databases and queries.
```toml
[dependencies]
entity = "0.3.0"
```
For most use cases, you will want to also import the macros, which will bring
in the `entity_macros` crate:
```toml
[dependencies]
entity = { version = "0.3.0", features = ["macros"] }
```
### Defining data using macros
The following is an example of defining a `User` data structure that contains
an _age_ and _name_ field as well as references to many other `User` instances
under the edge name _friends_.
```rust
use entity::simple_ent;
#[simple_ent]
struct User {
name: String,
age: u8,
#[ent(edge)]
friends: Vec<User>,
}
```
This generates a variety of trait implementations and additional data
structures to work with the `User` struct against any database.
#### Loading an ent by id
```rust
use entity::EntLoader;
let db = /* entity::WeakDatabaseRc instance */;
// Loads the user from the provided database reference
let user = User::load_from_db_strict(db, 123).expect("Database available");
// Loads the user from the globally-set database
let user = User::load_strict(123).expect("Database available");
```
#### Accessing ent fields
Every object implementing the `Ent` trait is able to access a variety of
common data including abstract field information:
```rust
use entity::{Ent, Primitive, Value};
let user = /* User instance */;
// Access a list of all field names
assert_eq!(user.field_names(), vec![String::from("name"), String::from("age")]);
// Access individual field values, which are exposed using entity's
// generic Value enum
assert_eq!(user.field("name"), Some(Value::Text(/* ... */)));
assert_eq!(user.field("age"), Some(Value::Primitive(Primitive::Number(/* ... */))));
```
When using macros to generate an ent, typed accessors are also provided as
seen below:
```rust
let user = /* User instance */;
// Accesses fields and returns a reference to their actual type NOT
// wrapped in entity's generic Value enum
assert_eq!(user.get_name(), &String::from("..."));
assert_eq!(user.get_age(), &123);
```
#### Accessing ent edges
Every object implementing the `Ent` trait is able to access a variety of
abstract edge information:
```rust
use entity::{Ent, EdgeValue};
let user = /* User instance */;
// Access a list of all edge names
assert_eq!(user.edge_names(), vec![String::from("friends")]);
// Access specific edge information (does not load it)
assert_eq!(user.edge("friends"), Some(EdgeValue::Many(vec![124, 125, /* ... */])));
// Load an edge by name, returning a Vec<Box<dyn Ent>>
let friends: Vec<Box<dyn Ent>> = user.load_edge("friends").expect("Database available");
```
When using macros to generate an ent, typed edge accessors are also provided
as seen below:
```rust
let user = /* User instance */;
// Access the ids of ents referenced by the edge
assert_eq!(user.my_friends_ids(), vec![124, 125, /* ... */]);
// Load the ents referenced by the edge into memory
let friends: Vec<User> = user.load_friends().expect("Database available");
```
#### Querying an ent
Alongside loading ents by their ids, the full suite that `entity-rs` provides
also includes the ability to query arbitrary data structures using a concept of
queries and associated predicates:
```rust
use entity::{EntQuery, Predicate as P, Query};
let db = /* WeakDatabaseRc instance */;
// Produce a new query to search for ents with an age field that is 18 or higher
let ents: Vec<Box<dyn Ent>> = Query::default()
.where_field("age", P::greater_than_or_equals(18))
.execute_with_db(db)
.expect("Database available");
// If the global database has been configured, can also be used in this manner
let ents: Vec<Box<dyn Ent>> = Query::default()
.where_field("age", P::greater_than_or_equals(18))
.execute()
.expect("Database available");
```
When using macros to generate an ent, a companion query struct that
provides stricter types on queries is also created using the name
`{Ent}Query`:
```rust
use entity::{EntQuery, TypedPredicate as P};
let db = /* WeakDatabaseRc instance */;
// Produce a new query to search for ents with an age field that is 18 or higher
let users: Vec<User> = User::query()
.where_age(P::greater_than_or_equals(18))
.execute_with_db(db)
.expect("Database available");
// If the global database has been configured, can also be used in this manner
let users: Vec<User> = User::query()
.where_age(P::greater_than_or_equals(18))
.execute()
.expect("Database available");
```
### Examples
* [`async-graphql`](integrations/entity-async-graphql/examples/user.rs):
example of using `entity-rs` with `async-graphql`
* [`inmemory`](integrations/entity-inmemory/examples/user.rs): example of using
`entity-rs` with a custom inmemory database
* [`sled`](integrations/entity-sled/examples/user.rs): example of using
`entity-rs` with `sled`
## Feature Flags
Entity provides a few feature flags:
* **`global`** - Enables use of a database stored as a global variable,
providing shortcuts in creating and retrieving ents.
* **`macros`** - Enables macros for deriving ents and exposing a cleaner
declarative API for ents. (Imports `entity_macros` directly)
* **`serde-1`** - Provides serde serialization module and associated functionality for ents
through the use of [typetag](https://github.com/dtolnay/typetag). This will
require that all ents implement [Serialize](https://docs.serde.rs/serde/trait.Serialize.html)
and [Deserialize](https://docs.serde.rs/serde/trait.Deserialize.html).
* Requires `serde` and `typetag` to be included in dependencies.