persistent-2.13.0.0: Type-safe, multi-backend data serialization.

Database.Persist.SqlBackend.Internal

Synopsis

# Documentation

A SqlBackend represents a handle or connection to a database. It contains functions and values that allow databases to have more optimized implementations, as well as references that benefit performance and sharing.

Instead of using the SqlBackend constructor directly, use the mkSqlBackend function.

A SqlBackend is *not* thread-safe. You should not assume that a SqlBackend can be shared among threads and run concurrent queries. This *will* result in problems. Instead, you should create a Pool SqlBackend, known as a ConnectionPool, and pass that around in multi-threaded applications.

To run actions in the persistent library, you should use the runSqlConn function. If you're using a multithreaded application, use the runSqlPool function.

Constructors

 SqlBackend FieldsconnPrepare :: Text -> IO StatementThis function should prepare a Statement in the target database, which should allow for efficient query reuse.connInsertSql :: EntityDef -> [PersistValue] -> InsertSqlResultThis function generates the SQL and values necessary for performing an insert against the database.connInsertManySql :: Maybe (EntityDef -> [[PersistValue]] -> InsertSqlResult)SQL for inserting many rows and returning their primary keys, for backends that support this functionality. If Nothing, rows will be inserted one-at-a-time using connInsertSql.connUpsertSql :: Maybe (EntityDef -> NonEmpty (FieldNameHS, FieldNameDB) -> Text -> Text)Some databases support performing UPSERT _and_ RETURN entity in a single call.This field when set will be used to generate the UPSERT+RETURN sql given * an entity definition * updates to be run on unique key(s) collisionWhen left as Nothing, we find the unique key from entity def before * trying to fetch an entity by said key * perform an update when result found, else issue an insert * return new entity from dbSince: 2.6connPutManySql :: Maybe (EntityDef -> Int -> Text)Some databases support performing bulk UPSERT, specifically "insert or replace many records" in a single call.This field when set, given * an entity definition * number of records to be inserted should produce a PUT MANY sql with placeholders for recordsWhen left as Nothing, we default to using defaultPutMany.Since: 2.8.1connStmtMap :: IORef (Map Text Statement)A reference to the cache of statements. Statements are keyed by the Text queries that generated them.connClose :: IO ()Close the underlying connection.connMigrateSql :: [EntityDef] -> (Text -> IO Statement) -> EntityDef -> IO (Either [Text] [(Bool, Text)])This function returns the migrations required to include the EntityDef parameter in the [EntityDef] database. This might include creating a new table if the entity is not present, or altering an existing table if it is.connBegin :: (Text -> IO Statement) -> Maybe IsolationLevel -> IO ()A function to begin a transaction for the underlying database.connCommit :: (Text -> IO Statement) -> IO ()A function to commit a transaction to the underlying database.connRollback :: (Text -> IO Statement) -> IO ()A function to roll back a transaction on the underlying database.connEscapeFieldName :: FieldNameDB -> TextA function to extract and escape the name of the column corresponding to the provided field.Since: 2.12.0.0connEscapeTableName :: EntityDef -> TextA function to extract and escape the name of the table corresponding to the provided entity. PostgreSQL uses this to support schemas.Since: 2.12.0.0connEscapeRawName :: Text -> TextA function to escape raw DB identifiers. MySQL uses backticks, while PostgreSQL uses quotes, and so on.Since: 2.12.0.0connNoLimit :: Text connRDBMS :: TextA tag displaying what database the SqlBackend is for. Can be used to differentiate features in downstream libraries for different database backends.connLimitOffset :: (Int, Int) -> Text -> TextAttach a 'LIMIT/OFFSET' clause to a SQL query. Note that LIMIT/OFFSET is problematic for performance, and indexed range queries are the superior way to offer pagination.connLogFunc :: LogFuncA log function for the SqlBackend to use.connMaxParams :: Maybe IntSome databases (probably only Sqlite) have a limit on how many question-mark parameters may be used in a statementSince: 2.6.1connRepsertManySql :: Maybe (EntityDef -> Int -> Text)Some databases support performing bulk an atomic+bulk INSERT where constraint conflicting entities can replace existing entities.This field when set, given * an entity definition * number of records to be inserted should produce a INSERT sql with placeholders for primary+record fieldsWhen left as Nothing, we default to using defaultRepsertMany.Since: 2.9.0

#### Instances

Instances details
A function for creating a value of the SqlBackend type. You should prefer to use this instead of the constructor for SqlBackend, because default values for this will be provided for new fields on the record when new functionality is added.