https://github.com/pickfire/diesel-join-not-exist
Rust diesel join not exist experiment
https://github.com/pickfire/diesel-join-not-exist
Last synced: 28 days ago
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Rust diesel join not exist experiment
- Host: GitHub
- URL: https://github.com/pickfire/diesel-join-not-exist
- Owner: pickfire
- Created: 2021-02-17T17:13:06.000Z (about 4 years ago)
- Default Branch: master
- Last Pushed: 2021-03-10T13:25:39.000Z (about 4 years ago)
- Last Synced: 2025-02-10T11:45:15.142Z (3 months ago)
- Language: Rust
- Size: 8.79 KB
- Stars: 0
- Watchers: 3
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
Diesel join not exist experiment
================================
Previous: https://github.com/pickfire/diesel-update-from
Next: https://github.com/pickfire/diesel-upsert
After getting footguns in sequelize and gorm, just want to try out diesel and
state of diesel.
I did not found a way to do left join where the other side does not exist, I
wanted to search a "has one" relationship where the parent table does not
have anything in the child table. But in gorm, I need to do a hack on `Joins`.
I think I started to get the hang of it. No wall crashing now, I just search
for "left join" and "null", then found `left_join` and `is_null` in the docs.
Tweak the original query, bingo! No surprise.
Seemed too easy now, maybe I need to try something harder next time. Probably
computed property or aggregation since I saw it could be done in diesel.
The example I tested out here have 3 struct (based on the previous ones).
sqlite was used for easy testing.
+---------+ +---------+ +---------+
| User |<-+ | Post | | Comment |
+---------+ | +---------+ +---------+
| id | | | id | | id |
| name | | | title | | body |
| | | | body |<----+ post_id |
| | | | user_id +--+--+ user_id |
+---------+ | +---------+ | +---------+
+---------------+
I want to find all posts that does not have any comments. The query,
```rust
let query = posts::table
.left_join(comments::table)
.select(posts::title)
.filter(comments::id.is_null());
```
Which results in the SQL query,
```sql
SELECT
`posts`.`title`
FROM (`posts`
LEFT OUTER JOIN `comments`
ON `comments`.`post_id` = `posts`.`id`)
WHERE `comments`.`id` IS NULL -- binds: []
```
## Get started
Rust, diesel_cli (with `sqlite` feature) is required.
```
$ diesel migration run
$ cargo run --bin init # populate database
$ cargo run --bin hello # multi join query
```