diff --git a/README.md b/README.md index ce32c92..203a1f0 100644 --- a/README.md +++ b/README.md @@ -1,26 +1,20 @@ -# Esqueleto +Esqueleto [![TravisCI](https://travis-ci.org/bitemyapp/esqueleto.svg)](https://travis-ci.org/bitemyapp/esqueleto) +========== -Esqueleto is a bare bones, type-safe EDSL for SQL queries that works with -unmodified persistent SQL backends. The name of this library means "skeleton" -in Portuguese and contains all three SQL letters in the correct order =). It -was inspired by Scala's Squeryl but created from scratch. Its language closely -resembles SQL. Currently, SELECTs, UPDATEs, INSERTs and DELETEs are supported. +![Skeleton](./esqueleto.png) +Image courtesy [Chrissy Long](https://www.flickr.com/photos/chrissylong/313800029/) -In particular, esqueleto is the recommended library for type-safe JOINs on -persistent SQL backends. (The alternative is using raw SQL, but that's error -prone and does not offer any composability.). For more information read -[esqueleto](http://hackage.haskell.org/package/esqueleto). +# Esqueleto, a SQL DSL for Haskell + +Esqueleto is a bare bones, type-safe EDSL for SQL queries that works with unmodified persistent SQL backends. The name of this library means "skeleton" in Portuguese and contains all three SQL letters in the correct order =). It was inspired by Scala's Squeryl but created from scratch. Its language closely resembles SQL. Currently, SELECTs, UPDATEs, INSERTs and DELETEs are supported. + +In particular, esqueleto is the recommended library for type-safe JOINs on persistent SQL backends. (The alternative is using raw SQL, but that's error prone and does not offer any composability.). For more information read [esqueleto](http://hackage.haskell.org/package/esqueleto). ## Setup -If you're already using `persistent`, then you're ready to use -`esqueleto`, no further setup is needed. If you're just -starting a new project and would like to use `esqueleto`, take -a look at `persistent`'s [book](http://www.yesodweb.com/book/persistent) first - to learn how to define your schema. +If you're already using `persistent`, then you're ready to use `esqueleto`, no further setup is needed. If you're just starting a new project and would like to use `esqueleto`, take a look at `persistent`'s [book](http://www.yesodweb.com/book/persistent) first to learn how to define your schema. -If you need to use `persistent`'s default support for queries -as well, either import it qualified: +If you need to use `persistent`'s default support for queries as well, either import it qualified: ```haskell -- For a module that mostly uses esqueleto. @@ -36,8 +30,7 @@ import Database.Persistent import qualified Database.Esqueleto as E ``` -Other than identifier name clashes, `esqueleto` does not -conflict with `persistent` in any way. +Other than identifier name clashes, `esqueleto` does not conflict with `persistent` in any way. ## Goals @@ -48,8 +41,7 @@ The main goals of `esqueleto` are: - Support the most widely used SQL features. - Be as type-safe as possible. -It is _not_ a goal to be able to write portable SQL. -We do not try to hide the differences between DBMSs from you +It is _not_ a goal to be able to write portable SQL. We do not try to hide the differences between DBMSs from you ## Introduction @@ -75,10 +67,7 @@ share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persist| ## Select -Most of `esqueleto` was created with `SELECT` statements in -mind, not only because they're the most common but also -because they're the most complex kind of statement. The most -simple kind of `SELECT` would be: +Most of `esqueleto` was created with `SELECT` statements in mind, not only because they're the most common but also because they're the most complex kind of statement. The most simple kind of `SELECT` would be: ```haskell putPersons :: SqlPersist m () @@ -96,8 +85,7 @@ SELECT * FROM Person ``` -`esqueleto` knows that we want an `Entity Person` just because of the `personName` that is -printed. +`esqueleto` knows that we want an `Entity Person` just because of the `personName` that is printed. ## Where @@ -118,10 +106,7 @@ FROM Person WHERE Person.name = "John" ``` -The `(^.)` operator is used to project a field from an entity. -The field name is the same one generated by `persistent`s -Template Haskell functions. We use `val` to lift a constant -Haskell value into the SQL query. +The `(^.)` operator is used to project a field from an entity. The field name is the same one generated by `persistent`s Template Haskell functions. We use `val` to lift a constant Haskell value into the SQL query. Another example: @@ -142,16 +127,13 @@ FROM Person WHERE Person.age >= 18 ``` -Since `age` is an optional `Person` field, we use `just` to lift -`val 18 :: SqlExpr (Value Int)` into `just (val 18) :: -SqlExpr (Value (Maybe Int))`. +Since `age` is an optional `Person` field, we use `just` to lift`val 18 :: SqlExpr (Value Int)` into `just (val 18) ::SqlExpr (Value (Maybe Int))`. ## Joins Implicit joins are represented by tuples. -For example, to get the list of all blog posts and their authors, we could -write: +For example, to get the list of all blog posts and their authors, we could write: ```haskell select $ @@ -171,8 +153,7 @@ ORDER BY BlogPost.title ASC ``` -However, you may want your results to include people who don't -have any blog posts as well using a `LEFT OUTER JOIN`: +However, you may want your results to include people who don't have any blog posts as well using a `LEFT OUTER JOIN`: ```haskell select $ @@ -193,17 +174,9 @@ ORDER BY Person.name ASC, BlogPost.title ASC ## Left Outer Join -On a `LEFT OUTER JOIN` the entity on the right hand side may -not exist (i.e. there may be a `Person` without any -`BlogPost`s), so while `p :: SqlExpr (Entity Person)`, we have -`mb :: SqlExpr (Maybe (Entity BlogPost))`. The whole -expression above has type `SqlPersist m [(Entity Person, Maybe -(Entity BlogPost))]`. Instead of using `(^.)`, we used -`(?.)` to project a field from a `Maybe (Entity a)`. +On a `LEFT OUTER JOIN` the entity on the right hand side may not exist (i.e. there may be a `Person` without any `BlogPost`s), so while `p :: SqlExpr (Entity Person)`, we have `mb :: SqlExpr (Maybe (Entity BlogPost))`. The whole expression above has type `SqlPersist m [(Entity Person, Maybe (Entity BlogPost))]`. Instead of using `(^.)`, we used `(?.)` to project a field from a `Maybe (Entity a)`. -We are by no means limited to joins of two tables, nor by -joins of different tables. For example, we may want a list -of the `Follow` entity: +We are by no means limited to joins of two tables, nor by joins of different tables. For example, we may want a list of the `Follow` entity: ```haskell select $ @@ -222,10 +195,7 @@ INNER JOIN Follow ON P1.id = Follow.follower INNER JOIN P2 ON P2.id = Follow.followed ``` -Note carefully that the order of the ON clauses is -reversed! You're required to write your `on`s in reverse -order because that helps composability (see the documentation -of `on` for more details). +Note carefully that the order of the ON clauses is reversed! You're required to write your `on`s in reverse order because that helps composability (see the documentation of `on` for more details). ## Update and Delete @@ -238,9 +208,7 @@ do update $ \p -> do where_ (p ^. PersonAge <. just (val 14)) ``` -The results of queries can also be used for insertions. -In `SQL`, we might write the following, inserting a new blog -post for every user: +The results of queries can also be used for insertions. In `SQL`, we might write the following, inserting a new blog post for every user: ```haskell insertSelect $ from $ \p-> @@ -255,28 +223,20 @@ SELECT ('Group Blog Post', id) FROM Person ``` -Individual insertions can be performed through Persistent's -`insert` function, reexported for convenience. +Individual insertions can be performed through Persistent's `insert` function, reexported for convenience. ### Re-exports We re-export many symbols from `persistent` for convenience: - "Store functions" from "Database.Persist". -- Everything from "Database.Persist.Class" except for - `PersistQuery` and `delete` (use `deleteKey` instead). -- Everything from "Database.Persist.Types" except for - `Update`, `SelectOpt`, `BackendSpecificFilter` and `Filter`. -- Everything from "Database.Persist.Sql" except for - `deleteWhereCount` and `updateWhereCount`. +- Everything from "Database.Persist.Class" except for `PersistQuery` and `delete` (use `deleteKey` instead). +- Everything from "Database.Persist.Types" except for `Update`, `SelectOpt`, `BackendSpecificFilter` and `Filter`. +- Everything from "Database.Persist.Sql" except for `deleteWhereCount` and `updateWhereCount`. ### RDBMS Specific -There are many differences between SQL syntax and functions -supported by different RDBMSs. Since version 2.2.8, -`esqueleto` includes modules containing functions that are -specific to a given RDBMS. +There are many differences between SQL syntax and functions supported by different RDBMSs. Since version 2.2.8, `esqueleto` includes modules containing functions that are specific to a given RDBMS. - PostgreSQL: `Database.Esqueleto.PostgreSQL` -In order to use these functions, you need to explicitly import -their corresponding modules +In order to use these functions, you need to explicitly import their corresponding modules. diff --git a/esqueleto.png b/esqueleto.png new file mode 100644 index 0000000..fbe51fa Binary files /dev/null and b/esqueleto.png differ