# AshNeo4j
[](https://hex.pm/packages/ash_neo4j)
[](https://hexdocs.pm/ash_neo4j/)
[](https://github.com/diffo-dev/ash_neo4j/blob/master/LICENSE.md)
Ash DataLayer for Neo4j, configurable using a simple DSL
## Installation
Add to the deps:
```elixir
def deps do
[
{:ash_neo4j, "~> 0.1.4"},
]
end
```
## Usage
Configure `AshNeo4j.DataLayer` as `data_layer:` within `use Ash.Resource` options:
```elixir
use Ash.Resource,
data_layer: AshNeo4j.DataLayer
```
### Configuration
Each Ash.Resource requires configuration of its AshNeo4j.DataLayer. An example Comment resource is given below, it can belong to a Post resource.
```elixir
defmodule Comment.Resource do
use Ash.Resource,
data_layer: AshNeo4j.DataLayer
neo4j do
label :Comment
relate [{:post, :BELONGS_TO, :outgoing}]
translate id: :uuid
end
actions do
default_accept(:*)
defaults([:create, :read, :update, :destroy])
end
attributes do
uuid_primary_key(:id)
attribute(:title, :string, public?: true)
end
relationships do
belongs_to(:post, Post, public?: true)
end
end
```
## Label
The DSL is used to label the Ash Resource's underlying graph node.
```elixir
neo4j do
label :Comment
end
```
## Relate
The DSL is used to direct any node relationships.
```elixir
neo4j do
relate [{:post, :BELONGS_TO, :outgoing}]
end
```
## Translate
The DSL may be used to translate the Ash Resource's attributes to node properties.
```elixir
neo4j do
translate id: :uuid
end
```
## Skip
The DSL may be used to skip storing attributes as node properties. This is typically used for foreign keys, which not required with relate.
```elixir
neo4j do
skip [:other_id]
end
```
## Verifiers
The DSL is verified against misconfiguration and violation of accepted neo4j conventions providing compile time errors:
* label: neo4j label must be CamelCase
* neo4j: neo4j property names should start with a letter and may contain numbers and underscores
* relate: relationship_name must match the name of a relationship
* relate: edge label must be upper case and may have an underscore
* translate: :id attribute must be translated
## Installing Neo4j and Configuring Boltx
ash_neo4j uses [neo4j](https://github.com/neo4j/neo4j) which must be installed and running.
Your Ash application needs to configure, start and supervise [boltx](https://github.com/sagastume/boltx), see [boltx documentation](https://hexdocs.pm/boltx/). Make sure to configure any required authorisation.
I've used Neo4j community edition 4.4 (bolt 4.4) and to connect using boltx I needed to also set the environment variable ```BOLT_VERSIONS=4.4``` to steer [bolt protocol handshake] (https://neo4j.com/docs/bolt/current/bolt/handshake).
## Elixir, Ash and Neo4j Types
We've made some decisions around how Ash/Elixir types are used to persist attributes as Neo4j properties. Where possible we've used 'native' Neo4j types, where this is not possible we've simply quoted to strings. Ash Array support is limited by Neo4j to lists of simple types which must be homogenous.
<style>
table th:first-of-type {
width: 10%;
}
table th:nth-of-type(2) {
width: 10%;
}
table th:nth-of-type(3) {
width: 10%;
}
table th:nth-of-type(4) {
width: 30%;
}
table th:nth-of-type(5) {
width: 30%;
}
table th:nth-of-type(46 {
width: 10%;
}
</style>
| Ash Type shortname | Ash Type Module | Elixir Type Module | Attribute Value Example | Neo4j Node Property Value Cypher Example | Cypher Type |
|---------------------|---------------------------|--------------------|--------------------------------------------------------|--------------------------------------------------------|----------------|
| :atom | Ash.Type.Atom | Atom | :a | ":a" | STRING |
| :binary | Ash.Type.Binary | BitString | <<1, 2, 3>> | "\u0001\u0002\u0003" | STRING |
| :boolean | Ash.Type.Boolean | Boolean | true | true | BOOLEAN |
| :integer | Ash.Type.Integer | Integer | 1 | 1 | INTEGER |
| :float | Ash.Type.Float | Float | 1.23456789 | 1.23456789 | FLOAT |
| :string | Ash.Type.String | BitString | "hello" | "hello" | STRING |
| :tuple | Ash.Type.Tuple | Tuple | \{:a, 1, false\} | "\{:a, 1, false\}" | STRING |
| :keyword | Ash.Type.Keyword | Keyword | [\{:a, :atom\}, \{:s, "string"\}] | ["\{:a, :atom}\","\{:s, string\}"] | LIST |
| :map | Ash.Type.Map | Map | %\{c: false, a: "a", b: 1, n: nil\} | "%\{c: false, a: "a", b: 1, n: nil\}" | STRING |
| :mapset | Ash.Type.MapSet | MapSet | MapSet.new([1, false, :two]) | "MapSet.new([1, false, :two])" | STRING |
| :struct | Ash.Type.Struct | Struct | %MyApp.Struct{a: :a, s: "Hello"} | "%MyApp.Struct\{a: :a, s: \"Hello\"\}" | STRING |
| :uuid | Ash.Type.UUID | BitString | "0274972c-161c-4dc9-882f-6851704c2af9" | "0274972c-161c-4dc9-882f-6851704c2af9 | STRING |
| :url_encoded_binary | Ash.Type.UrlEncodedBinary | BitString | "aHR0cHM6Ly93d3cuZGlmZm8uZGV2Lw" | "aHR0cHM6Ly93d3cuZGlmZm8uZGV2Lw | STRING |
| :decimal | Ash.Type.Decimal | Decimal | Decimal.new("4.2") | "Decimal.new(\"4.2\")" | STRING |
| :ci_string | Ash.Type.CiString | BitString | "HELLO" | "HELLO" | STRING |
| :function | Ash.Type.Function | Function | &AshNeo4j.Neo4jHelper.create_node/2 | "&AshNeo4j.Neo4jHelper.create_node/2" | STRING |
| :module | Ash.Type.Module | Module | AshNeo4j.DataLayer | ":Elixir.AshNeo4j.DataLayer" | STRING |
| :regex | Ash.Type.Regex | Regex | ~r/foo/iu | "~r/foo/iu" | STRING |
| \{:array, :atom\} | - | List | [:a,:b,:c] | [":a",":b",":c"] | LIST |
| \{:array, :boolean\} | - | List | [true,true,false] | [true,true,false] | LIST |
| \{:array, :integer\} | - | List | [1,2,3] | [1,2,3] | LIST |
| \{:array, :map\} | - | List | [%MyApp.Struct\{a: :a, s: "Hello"\}] | ["%MyApp.Struct\{a: :a, s: \"Hello\"\}"] | LIST |
| \{:array, :term\} | - | List | [%MyApp.Struct\{a: :a, s: "Hello"\}] | ["%MyApp.Struct\{a: :a, s: \"Hello\"\}"] | LIST |
| :date | Ash.Type.Date | Date | ~D[2025-02-25] | 2025-05-11 | DATE |
| :datetime | Ash.Type.DateTime | DateTime | ~U[2025-02-25 11:59:00Z] | 2025-05-11T07:45:41Z | ZONED_DATETIME |
| :utc_datetime_usec | Ash.Type.UtcDateTimeUsec | DateTime | ~U[2025-02-25 11:59:00.123456Z] | 2025-05-11T07:45:41.429903Z | ZONED_DATETIME |
| :naive_datetime | Ash.Type.NaiveDateTime | NaiveDateTime | ~N[2025-05-11 07:45:41] | 2025-05-11T07:45:41 | LOCAL_DATETIME |
| :time | Ash.Type.Time | Time | ~T[07:45:41Z] | 07:45:41 | TIME |
| :time_usec | Ash.Type.TimeUsec | Time | ~T[07:45:41.429903Z] | 07:45:41.429903 | TIME |
| :duration | Ash.Type.Duration | Duration | %Duration{month: 2} | PT2H | DURATION |
Ash :date, :datetime, :time and :naive_datetime are second precision, whereas :utc_datetime_usec and :time_usec are microsecond precision. Note that :time_usec requires ash ~> 3.5.10 (to be released).
## Elixir nil and Neo4j Null
Generally attributes with nil value are not persisted, rather than created with Null value. However values of nil within string quoted 'Elixir' types (keyword, tuple, map and struct) are persisted.
## Limitations and Future Work
Ash Neo4j is early stage, it is likely that the dsl will evolve and this may break back compatibility. Store is likely to be removed in favour of introspecting resource attributes. The dsl lacks validation and doesn't yet make appropriate use of transform.
Currently ash_neo4j has limited support for Ash create, update, read, destroy actions, and is in 'build' phase.
Collaboration on ash_neo4j welcome via github, please use discussions and/or issues as appropriate.
## Acknowledgements
Thanks to the [Ash Core](https://github.com/ash-project) for [ash](https://github.com/ash-project/ash) 🚀, including [ash_csv](https://github.com/vonagam/ash_jason) which was an exemplar.
Thanks to [Sagastume](https://github.com/sagastume) for [boltx](https://github.com/tiagodavi/ex4j) which AFAIK was based on [bolt_sips](https://github.com/florinpatrascu/bolt_sips) by [Florin Patrascu](https://github.com/florinpatrascu).
Thanks to the [Neo4j Core](https://github.com/neo4j) for [neo4j](https://github.com/neo4j/neo4j) and pioneering work on graph databases.
## Links
[Diffo.dev](https://www.diffo.dev)
[Neo4j Deployment Centre](https://neo4j.com/deployment-center/).
