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https://github.com/caneroj1/sqlite-simple-errors
Light wrapper around errors from sqlite-simple to make working with constraint errors a bit easier.
https://github.com/caneroj1/sqlite-simple-errors
error-handling haskell sqlite
Last synced: about 1 month ago
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Light wrapper around errors from sqlite-simple to make working with constraint errors a bit easier.
- Host: GitHub
- URL: https://github.com/caneroj1/sqlite-simple-errors
- Owner: caneroj1
- License: bsd-3-clause
- Created: 2016-10-09T18:00:49.000Z (over 8 years ago)
- Default Branch: master
- Last Pushed: 2020-06-18T17:11:55.000Z (over 4 years ago)
- Last Synced: 2024-04-24T22:21:47.506Z (9 months ago)
- Topics: error-handling, haskell, sqlite
- Language: Haskell
- Size: 22.5 KB
- Stars: 5
- Watchers: 2
- Forks: 4
- Open Issues: 3
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# sqlite-simple-errors
Hackage
[](https://travis-ci.org/caneroj1/sqlite-simple-errors)
Light wrapper around errors from sqlite-simple to make working with constraint errors a bit easier.
The wrapper function, ```runDBAction``` allows you to run your database code and get the errors returned to you:
```haskell
type DatabaseResponse a = Either SQLiteResponse a
runDBAction :: IO a -> IO (DatabaseResponse a)
```
```SQLiteResponse``` encapsulates the different error types that can be thrown by sqlite-simple, as well as providing a new error type for constraint violations that is more immediately actionable:
```haskell
data Constraint = NotNull
| ForeignKey
| Unique
| Check
deriving (Show, Eq)
data SQLiteResponse = SQLConstraintError Constraint Text
| SQLFormatError FormatError
| SQLResultError ResultError
| SQLOtherError SQLError
deriving (Show, Eq, Typeable)
```
## Usage
Let's use sqlite-simple to create our ```People``` table.
```haskell
createPeopleTableSQL :: Query
createPeopleTableSQL =
"CREATE TABLE if not exists People (name varchar(50) NOT NULL UNIQUE \
\ ,age int CHECK(age > 0) \
\ ,id integer PRIMARY KEY NOT NULL); "
```
### Not Null Constraint
If we try to insert a record into our database where we provide a ```NULL``` value on a column that is ```NOT NULL```:
```haskell
result <- runDBAction $ execute conn "INSERT INTO People (name, age) VALUES (?, ?)" ( (Nothing, 10) :: (Maybe Text, Int) )
```
where ```result``` is ```Left $ SQLConstraintError NotNull "People.name"```.
The typical error you would get from ```sqlite-simple``` would be a ```SQLError``` whose error context is ```"SQLite3 returned ErrorConstraint while attempting to perform step: NOT NULL constraint failed: People.name"```.
### Unique Constraint
If we try to insert a record into our database that violates a ```UNIQUE``` constraint:
```haskell
_ <- runDBAction $ execute conn "INSERT INTO People (name, age) VALUES (?, ?)" ( ("Joe", 10) :: (Text, Int) )
result <- runDBAction $ execute conn "INSERT INTO People (name, age) VALUES (?, ?)" ( ("Joe", 10) :: (Text, Int) )
```
where ```result``` is ```Left $ SQLConstraintError Unique "People.name"```.
The typical error you would get from ```sqlite-simple``` would be a ```SQLError``` whose error context is ```"SQLite3 returned ErrorConstraint while attempting to perform step: UNIQUE constraint failed: People.name"```.
### Check Constraint
If we try to insert a record that violates some condition we've specified through ```CHECK```:
```haskell
result <- runDBAction $ execute conn "INSERT INTO People (name, age) VALUES (?, ?)" ( ("Joe", 0) :: (Text, Int) )
```
where ```result``` is ```Left $ SQLConstraintError Check "People"```.
The typical error you would get from ```sqlite-simple``` would be a ```SQLError``` whose error context is ```"SQLite3 returned ErrorConstraint while attempting to perform step: CHECK constraint failed: People"```.
### Foreign Key Constraint
Let's make a new table where we can have a foreign key.
```haskell
createJobsTableSQL :: Query
createJobsTableSQL =
"CREATE TABLE if not exists Jobs (title varchar(50) \
\ ,person_id int NOT NULL \
\ ,FOREIGN KEY(person_id) REFERENCES People(id)); "
```
If we try to insert a record into this table without a corresponding entry in the People table:
```haskell
result <- runDBAction $ execute conn "INSERT INTO Jobs (title, person_id) VALUES (?, ?)" (("coder", -1) :: (Text, Int))
```
where ```result``` is ```Left $ SQLConstraintError ForeignKey ""```.
The typical error you would get from ```sqlite-simple``` would be a ```SQLError``` whose error context is ```"SQLite3 returned ErrorConstraint while attempting to perform step: FOREIGN KEY constraint failed"```.