Orville.PostgreSQL.Execution.Select

Functions for working with executable SELECT statements. The Select type is a value that can be passed around and executed later. The Select is directly associated with how to decode the rows returned by the query. This means it can be safely executed via executeSelect and used to decode the rows. It is a lower-level API than the entity select functions in Orville.PostgreSQL.Execution.EntityOperations, but not as primitive as Orville.PostgreSQL.Expr.Query.

Since: 1.0.0.0

Documentation

data Select readEntity

Represents a SELECT statement that can be executed against a database. A Select has a SqlMarshaller bound to it that will be used to decode the database result set when it is executed.

Since: 1.0.0.0

executeSelect :: MonadOrville m => Select row -> m [row]

Executes the database query for the Select and uses its SqlMarshaller to decode the result set.

Since: 1.0.0.0

useSelect :: (forall writeEntity. QueryExpr -> AnnotatedSqlMarshaller writeEntity readEntity -> a) -> Select readEntity -> a

Runs a function allowing it to use the data elements containted within the Select it pleases. The marshaller that the function is provided can be use to decode results from the query.

Since: 1.0.0.0

selectToQueryExpr :: Select readEntity -> QueryExpr

Extracts the query that will be run when the select is executed. Normally you don't want to extract the query and run it yourself, but this function is useful to view the query for debugging or query explanation.

Since: 1.0.0.0

selectTable :: TableDefinition key writeEntity readEntity -> SelectOptions -> Select readEntity

Builds a Select that will select all the columns described in the TableDefinition. This is the safest way to build a Select, because table name and columns are all read from the TableDefinition. If the table is being managed with Orville auto-migrations, this will match the schema in the database.

Since: 1.0.0.0

selectMarshalledColumns :: AnnotatedSqlMarshaller writeEntity readEntity -> Qualified TableName -> SelectOptions -> Select readEntity

Builds a Select that will select the columns described by the marshaller from the specified table. It is up to the caller to ensure that the columns in the marshaller make sense for the table.

This function is useful for querying a subset of table columns using a custom marshaller.

Since: 1.0.0.0

rawSelectQueryExpr :: AnnotatedSqlMarshaller writeEntity readEntity -> QueryExpr -> Select readEntity

Builds a Select that will execute the specified query and use the given SqlMarshaller to decode it. It is up to the caller to ensure that the given QueryExpr makes sense and produces a result set that the SqlMarshaller can decode.

This is the lowest level of escape hatch available for Select. The caller can build any query that Orville supports using the expression-building functions, or use RawSql.fromRawSql to build a raw QueryExpr.

Since: 1.0.0.0