# Predicated
[](https://github.com/themusicman/predicated/actions/workflows/elixir.yml)
Predicated is a library that allows for building predicates to query an in-memory data structure in Elixir.
## Installation
If [available in Hex](https://hex.pm/packages/predicated), the package can be installed
by adding `predicated` to your list of dependencies in `mix.exs`:
```elixir
def deps do
[
{:predicated, "~> 1.0"}
]
end
```
## Examples
Using Structs.
```elixir
predicates = [
%Predicate{
condition: %Condition{
identifier: "last_name",
comparison_operator: "==",
expression: "Armstrong"
},
logical_operator: :and
},
%Predicate{
predicates: [
%Predicate{
condition: %Condition{
identifier: "first_name",
comparison_operator: "==",
expression: "Joe"
},
logical_operator: :or
},
%Predicate{
predicates: [
%Predicate{
condition: %Condition{
identifier: "first_name",
comparison_operator: "==",
expression: "Jill"
},
logical_operator: :and
},
%Predicate{
condition: %Condition{
identifier: "first_name",
comparison_operator: "==",
expression: "Joe"
}
}
]
}
],
logical_operator: :and
},
%Predicate{
condition: %Condition{
identifier: "last_name",
comparison_operator: "==",
expression: "Beaver"
}
}
]
# true && (true || (false && true)) && false
assert Predicated.test(predicates, %{first_name: "Joe", last_name: "Armstrong"}) == false
```
The example above could also be written with just plain maps or embedded schema as long as the data shape is the same.
For example
```elixir
%Predicate{
condition: %Condition{
identifier: "last_name",
comparison_operator: "==",
expression: "Beaver"
}
}
```
converted to a map would be
```elixir
%{
condition: %{
identifier: "last_name",
comparison_operator: "==",
expression: "Beaver"
}
}
```
Using a query string:
```elixir
assert Predicated.test("trace_id != 'test123' and profile_id == '123'", %{
trace_id: "test123",
profile_id: "123"
}) == false
```
Support for grouped and nested predicates:
```elixir
assert Predicated.test("organization_id == '123' AND (user_id == '123' OR user_id == '456' OR (user_type == 'admin' OR user_type == 'editor'))", %{
organization_id: "123",
user_id: "767",
user_type: "admin"
}) == true
```
Support for boolean and integers:
```elixir
assert Predicated.test("verified == TRUE AND post.count > 100", %{
verified: true,
post: %{ count: 123 }
}) == true
```
Support for dates and datetimes:
```elixir
assert Predicated.test("dob >= '2020-01-01'::DATE", %{
dob: ~D[2023-02-11]
}) == true
```
```elixir
assert Predicated.test("inserted_at >= '2020-01-01T01:50:07Z'::DATETIME", %{
inserted_at: ~U[2020-01-01 10:00:00Z]
}) == true
```
## TODO
- [x] Implement grouped/nested predicates in the query parser
- [ ] Add a to_sql function that turns the predicate data structure into where clauses in an ecto query
- [ ] Better handle non-terminal conditions when predicates are malformed
- [ ] Add debugger that displays all the conditions and their results
- [ ] Update docs to include example of using Ecto to store the predicates
- [ ] More tests
Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
be found at <https://hexdocs.pm/predicated>.
