mirror of
https://github.com/ash-project/ash_postgres.git
synced 2024-09-20 13:33:50 +12:00
38eec0ba86
improvement: support `mix ash.rollback` with interactive rollback
77 lines
2 KiB
Markdown
77 lines
2 KiB
Markdown
# Expressions
|
|
|
|
In addition to the expressions listed in the [Ash expressions guide](https://hexdocs.pm/ash/expressions.html), AshPostgres provides the following expressions
|
|
|
|
# Fragments
|
|
|
|
Fragments allow you to use arbitrary postgres expressions in your queries. Fragments can often be an escape hatch to allow you to do things that don't have something officially supported with Ash.
|
|
|
|
### Examples
|
|
|
|
#### Simple expressions
|
|
|
|
```elixir
|
|
fragment("? / ?", points, count)
|
|
```
|
|
|
|
#### Calling functions
|
|
|
|
```elixir
|
|
fragment("repeat('hello', 4)")
|
|
```
|
|
|
|
#### Using entire queries
|
|
|
|
```elixir
|
|
fragment("points > (SELECT SUM(points) FROM games WHERE user_id = ? AND id != ?)", user_id, id)
|
|
```
|
|
|
|
> ### a last resport {: .warning}
|
|
>
|
|
> Using entire queries as shown above is a last resort, but can sometimes be the best way to accomplish a given task.
|
|
|
|
#### In calculations
|
|
|
|
```elixir
|
|
calculations do
|
|
calculate :lower_name, :string, expr(
|
|
fragment("LOWER(?)", name)
|
|
)
|
|
end
|
|
```
|
|
|
|
#### In migrations
|
|
|
|
```elixir
|
|
create table(:managers, primary_key: false) do
|
|
add :id, :uuid, null: false, default: fragment("UUID_GENERATE_V4()"), primary_key: true
|
|
end
|
|
```
|
|
|
|
## Like and ILike
|
|
|
|
These wrap the postgres builtin like and ilike operators.
|
|
|
|
Please be aware, these match *patterns* not raw text. Use `contains/1` if you want to match text without supporting patterns, i.e `%` and `_` have semantic meaning!
|
|
|
|
For example:
|
|
|
|
```elixir
|
|
Ash.Query.filter(User, like(name, "%obo%")) # name contains obo anywhere in the string, case sensitively
|
|
```
|
|
|
|
```elixir
|
|
Ash.Query.filter(User, ilike(name, "%ObO%")) # name contains ObO anywhere in the string, case insensitively
|
|
```
|
|
|
|
## Trigram similarity
|
|
|
|
To use this expression, you must have the `pg_trgm` extension in your repos `installed_extensions` list.
|
|
|
|
This calls the `similarity` function from that extension. See more https://www.postgresql.org/docs/current/pgtrgm.htmlhere: https://www.postgresql.org/docs/current/pgtrgm.html
|
|
|
|
For example:
|
|
|
|
```elixir
|
|
Ash.Query.filter(User, trigram_similarity(first_name, "fred") > 0.8)
|
|
```
|