package caqti-lwt

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package caqti-lwt
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The connection API specialized for the current concurrency library.

include Caqti_connection_sig.Base with type 'a future := 'a Lwt.t

Query

module Response : Caqti_response_sig.S with type 'a future := 'a Lwt.t
val call : f:(('b, 'm) Response.t -> ('c, 'e) result Lwt.t) -> ('a, 'b, 'm) Caqti_request.t -> 'a -> ('c, [> Caqti_error.call ] as 'e) result Lwt.t

call ~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 Lwt.t

Starts a transaction if supported by the underlying database, otherwise does nothing.

val commit : unit -> (unit, [> Caqti_error.transact ]) result Lwt.t

Commits the current transaction if supported by the underlying database, otherwise does nothing.

val rollback : unit -> (unit, [> Caqti_error.transact ]) result Lwt.t

Rolls back a transaction if supported by the underlying database, otherwise does nothing.

Disconnection and Reuse

val disconnect : unit -> unit Lwt.t

Calling disconnect () closes the connection to the database and frees up related resources.

val validate : unit -> bool Lwt.t

For internal use by Caqti_pool. Tries to ensure the validity of the connection and must return false if unsuccessful.

val check : (bool -> unit) -> unit

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.t

Information 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 Lwt.t

Combining 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 Lwt.t

Combining 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 Lwt.t

Combining 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 Lwt.t

Combining 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 Lwt.t) -> 'a -> 'c -> ('c, [> Caqti_error.call_or_retrieve ] as 'e) result Lwt.t

Combining 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 Lwt.t) -> 'a -> (unit, [> Caqti_error.call_or_retrieve ] as 'e) result Lwt.t

Combining 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 Lwt.t

collect_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 Lwt.t

rev_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.