generated from tpl/purs
154 lines
5.3 KiB
Markdown
154 lines
5.3 KiB
Markdown
# purescript-postgresql-client
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purescript-postgresql-client is a PostgreSQL client library for PureScript.
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## Install
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To use this library, you need to add [`pg`][pg] and [`decimal.js`][decimal.js] as an npm dependency. You can also
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find first of them on [https://github.com/brianc/node-postgres](https://github.com/brianc/node-postgres).
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## Usage
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This guide is a literate Purescript file which is extracted into testing module (using [`literate-purescript`](https://github.com/Thimoteus/literate-purescript)) so it is a little verbose.
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Let's start with imports.
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```purescript
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module Test.README where
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import Prelude
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import Database.PostgreSQL.PG (defaultPoolConfiguration, command, execute, newPool, PG, query, Query(Query), withConnection, withTransaction)
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import Database.PostgreSQL.Row (Row0(Row0), Row3(Row3))
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import Data.Decimal as Decimal
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import Data.Maybe (Maybe(..))
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import Data.Tuple.Nested ((/\))
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import Effect.Class (liftEffect)
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import Test.Assert (assert)
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```
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The whole API for interaction with PostgreSQL is performed asynchronously in `Aff`
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(the only function which runs in plain `Effect` is `newPool`). To be honest we
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are wrapping `Aff` in `ExceptT` so you can easily handle database related errors
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in a sane manner:
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```purescript
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type PG a = ExceptT PGError Aff a
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```
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Don't be scarred by this `PG` type alias. It just wraps every db result in `Either`.
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You can turn `PG a` into the `Aff (Either PGError a)` by just running a single
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function - `runExceptT`.
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We assume here that postgres is running on a standard local port
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with `ident` authentication so configuration can be nearly empty (`defaultPoolConfiguration`).
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It requires only database name which we pass to `newPool` function.
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We setup also `idleTimeoutMillis` value because this code
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is run by our test suite and we want to exit after its execution quickly ;-)
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```purescript
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run ∷ PG Unit
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run = do
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pool <- liftEffect $ newPool
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((defaultPoolConfiguration "purspg") { idleTimeoutMillis = Just 1000 })
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withConnection pool \conn -> do
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```
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We can now create our temporary table which we are going to query in this example.
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`execute` ignores result value which is what we want in this case.
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The last `Row0` value indicates that this `Query` doesn't take any additional parameters.
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```purescript
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execute conn (Query """
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CREATE TEMPORARY TABLE fruits (
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name text NOT NULL,
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delicious boolean NOT NULL,
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price NUMERIC(4,2) NOT NULL,
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added TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT CURRENT_TIMESTAMP,
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PRIMARY KEY (name)
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);
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""") Row0
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```
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There is `withTransaction` helper provided. You can wrap the whole
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piece of interaction with database in it. It will rollback if any exception
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is thrown during execution of a given `Aff` block. It excecutes `COMMIT`
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in the other case.
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We start our session with insert of some data. It is done by `execute`
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function with `INSERT` statement.
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Please notice that we are passing a tuple of the arguments to this query
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using dedicated constructor. In this case `Row3`. This library provides types
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from `Row0` to `Row19` and they are wrappers which provide instances for
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automatic conversions from and to SQL values.
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For details please check following classes `ToSQLRow`, `ToSQLValue`,
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`FromSQLRow` and `FromSQLValue`.
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```purescript
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withTransaction conn $ do
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execute conn (Query """
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INSERT INTO fruits (name, delicious, price)
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VALUES ($1, $2, $3)
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""") (Row3 "coconut" true (Decimal.fromString "8.30"))
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```
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We can also use nested tuples instead of `Row*` constructors. This can be a bit more
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verbose but is not restricted to limited and constant number of arguments.
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`/\` is just an alias for the `Tuple` constructor from `Data.Tuple.Nested`.
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```purescript
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execute conn (Query """
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INSERT INTO fruits (name, delicious, price)
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VALUES ($1, $2, $3)
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""") ("lemon" /\ false /\ Decimal.fromString "3.30")
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```
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Of course `Row*` types and nested tuples can be also used when we are fetching
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data from db.
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`query` function processes db response and returns an `Array` of rows.
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```purescript
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names <- query conn (Query """
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SELECT name, delicious
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FROM fruits
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ORDER BY name ASC
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""") Row0
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liftEffect <<< assert $ names == ["coconut" /\ true, "lemon" /\ false]
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```
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There is also a `command` function at our disposal.
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Some postgres SQL expressions return a "command tag" which carries
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a value with a number of rows which were affected by a given query.
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For example we can have: `DELETE rows`, `UPDATE rows`, `INSERT oid rows` etc.
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This function should return `rows` value associated with given response.
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```purescript
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deleted <- command conn (Query """DELETE FROM fruits """) Row0
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liftEffect <<< assert $ deleted == 2
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```
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## Testing
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Currently tests are prepared to work with default and local setup for postgresql (ident authentication, standart port etc.).
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If you think that we should add configuration layer for our test runner please open an issue.
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To run suite please:
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* `$ npm install`
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* `$ createdb purspg`
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* `$ npm run test`
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## Generating SQL Queries
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The purspgpp preprocessor has been replaced by [sqltopurs], which is a code
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generator instead of a preprocessor, and easier to use.
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[sqltopurs]: https://github.com/rightfold/sqltopurs
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[pg]: https://www.npmjs.com/package/pg
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[decimal.js]: https://www.npmjs.com/package/decimal.js
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