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package caqti-async
The connection API specialized for the current concurrency library.
include Caqti_connection_sig.Base with type 'a future := 'a Async.Deferred.t
Query
module Response :
Caqti_response_sig.S with type 'a future := 'a Async.Deferred.tval call :
f:(('b, 'm) Response.t -> ('c, 'e) result Async.Deferred.t) ->
('a, 'b, 'm) Caqti_request.t ->
'a ->
('c, [> Caqti_error.call ] as 'e) result Async.Deferred.tcall ~f request params performs request with parameters params invoking f to process the result. The argument of f is only valid during the call to f, and must not be returned or operated on by other threads.
Transactions
val start : unit -> (unit, [> Caqti_error.transact ]) result Async.Deferred.tStarts a transaction if supported by the underlying database, otherwise does nothing.
val commit : unit -> (unit, [> Caqti_error.transact ]) result Async.Deferred.tCommits the current transaction if supported by the underlying database, otherwise does nothing.
val rollback :
unit ->
(unit, [> Caqti_error.transact ]) result Async.Deferred.tRolls back a transaction if supported by the underlying database, otherwise does nothing.
Disconnection and Reuse
val disconnect : unit -> unit Async.Deferred.tCalling disconnect () closes the connection to the database and frees up related resources.
val validate : unit -> bool Async.Deferred.tFor internal use by Caqti_pool. Tries to ensure the validity of the connection and must return false if unsuccessful.
For internal use by Caqti_pool. Called after a connection has been used. check f must call f () exactly once with an argument indicating whether to keep the connection in the pool or discard it.
val driver_info : Caqti_driver_info.tInformation about the driver providing this connection module.
Retrieval Convenience
These are shortcuts for call combined with retrieval functions from Caqti_response_sig.S of the same name.
val exec :
('a, unit, [< `Zero ]) Caqti_request.t ->
'a ->
(unit, [> Caqti_error.call_or_retrieve ] as 'e) result Async.Deferred.tCombining call with Response.exec, this sends a request to the database and checks that no rows are returned.
val find :
('a, 'b, [< `One ]) Caqti_request.t ->
'a ->
('b, [> Caqti_error.call_or_retrieve ] as 'e) result Async.Deferred.tCombining call with Response.find, this sends a request to the database, checks that a single row is returned, and extracts it.
val find_opt :
('a, 'b, [< `Zero | `One ]) Caqti_request.t ->
'a ->
('b option, [> Caqti_error.call_or_retrieve ] as 'e) result Async.Deferred.tCombining call with Response.find_opt, this sends a request to the database, checks that at most one row is returned, and extracts it if present.
val fold :
('a, 'b, [< `Zero | `One | `Many ]) Caqti_request.t ->
('b -> 'c -> 'c) ->
'a ->
'c ->
('c, [> Caqti_error.call_or_retrieve ] as 'e) result Async.Deferred.tCombining call with Response.fold, this sends a request to the database and folds over the result rows.
val fold_s :
('a, 'b, [< `Zero | `One | `Many ]) Caqti_request.t ->
('b -> 'c -> ('c, 'e) result Async.Deferred.t) ->
'a ->
'c ->
('c, [> Caqti_error.call_or_retrieve ] as 'e) result Async.Deferred.tCombining call with Response.fold_s, this sends a request to the database and folds concurrently over the result rows.
Please be aware of possible deadlocks when using resources from the callback. In particular, if the same connection pool is invoked as the one used to obtain the current connection, it will deadlock if the pool has just run out of connections. An alternative is to collect the rows first e.g. with fold and do the nested queries after exiting.
val iter_s :
('a, 'b, [< `Zero | `One | `Many ]) Caqti_request.t ->
('b -> (unit, 'e) result Async.Deferred.t) ->
'a ->
(unit, [> Caqti_error.call_or_retrieve ] as 'e) result Async.Deferred.tCombining call with Response.iter_s, this sends a request to the database and iterates concurrently over the result rows. Please see the warning in fold_s about resource usage in the callback.
val collect_list :
('a, 'b, [< `Zero | `One | `Many ]) Caqti_request.t ->
'a ->
('b list, [> Caqti_error.call_or_retrieve ] as 'e) result Async.Deferred.tcollect_list request param performs a call on request, extracting the result as a list.
val rev_collect_list :
('a, 'b, [< `Zero | `One | `Many ]) Caqti_request.t ->
'a ->
('b list, [> Caqti_error.call_or_retrieve ] as 'e) result Async.Deferred.trev_collect_list request param performs a call on request, extracting the result as a reversed list. This is more efficient than find_list and fits well with a subsequent List.rev_map, though it may not matter much in practise.
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