package caqti

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Module type
Class type

Standard type descriptors provided as a submodule for easy inclusion.

Field Types

The following types correspond to what usually fits in a single field of a result row or input parameter set.

val bool : bool t

A bool mapped to boolean on the SQL side if supported, otherwise mapped to an integer.

val int : int t

An int mapped to a sufficiently wide integer on the SQL side.

val int16 : int t

An int mapped to a smallint (16 bits) on the SQL side.

val int32 : int32 t

An int32 mapped to an integer (32 bits) on the SQL side.

val int64 : int64 t

An int64 mapped to a bigint (64 bits) on the SQL side.

val float : float t

A float mapped to double precision or (best alternative) on the SQL side. Serialization may be lossy (e.g. base 10 may be used), so even if both sides support IEEE 754 double precision numbers, there may be discrepancies in the last digits of the binary representaton.

val string : string t

An UTF-8 string. The database should accept UTF-8 if non-ASCII characters are present.

val octets : string t

A string mapped to whichever type is used to represent binary data on the SQL side.

val pdate : Ptime.t t

A time truncated to a date and mapped to the SQL date type.

val ptime : Ptime.t t

An absolute time with driver-dependent precision. This corresponds to an SQL timestamp with time zone or a suitable alternative where not available:

  • MariaDB has datetime which is similar to the SQL timestamp and timestamp which is similar to the SQL timestamp with time zone, but the driver does not make the distinction. Caqti sets the session time zone to UTC to avoid misinterpretation, since time values are passed in both directions without time zones. Values have microsecond precision, but you will need to specify the desired precision in the database schema to avoid truncation.
  • PostgreSQL supports this type and it's a good option to avoid any time zone issues if used conistently both on the client side, in SQL expressions, and in the database schema. Note that timestamp with time zone is stored as UTC without time zone, taking up no more space then timestamp. The PostgreSQL timestamp type is problematic since how conversions work and the manual indicate that it is meant to be a local time, and since database columns of this type stores the value without conversion to UTC, it becomes prone to time zone changes. To mitigate the issue, Caqti sets the time zone of sessions to UTC.
  • Sqlite3 does not have a dedicated type for absolute time. The date and time is sent as strings expressed at the UTC time zone using same format that the SQLite datetime function and CURRENT_TIMESTAMP return, except for an additional three decimals to achive millisecond precision.

It might seem better to use standard RFC3339 format, since it is accepted by the SQLite functions, but that would misorder some time values if mixed with the results of these functions, even just the "Z" suffix would misorder values with different precision.

Date and time values which comes from the database without time zone are interpreted as UTC. This is not necessarily correct, and it is highly recommended to use SQL types which are transmitted with time zone information, even if this is UTC.

val ptime_span : Ptime.span t

A period of time. If the database lacks a dedicated representation, the integer number of seconds is used.

val enum : encode:('a -> string) -> decode:(string -> ('a, string) Stdlib.result) -> string -> 'a t

enum ~encode ~decode name creates an enum type which on the SQL side is named name, with cases which are converted with encode and decode functions. This is implemented in terms of the Caqti_type.Field.t.Enum field type.

Composite Types

val product : 'i -> ('a, 'i) product -> 'a t
val proj : 'b t -> ('a -> 'b) -> ('a, 'i) product -> ('a, 'b -> 'i) product
val proj_end : ('a, 'a) product

Given a set of projection functions p1 : t -> t1, ..., pN : t -> tN and a function intro : t1 -> ... -> tN -> t to reconstruct values of t from the projections,

product intro
  @@ proj t1 p1
  @@ ...
  @@ proj tN pN
  @@ proj_end

defines a Caqti type for t, which on the database side will be represented by a consecutive list of fields corresponding to the types t1, ..., tN, each of which may be represented by multiple fields. That is, intro [project1 x] ... [projectN x] is equivalent to x according to an enforced or effective abstraction of t deemed adequate for the application logic.

intro may raise Caqti_type.Reject to indicate that a value cannot be constructed from the given arguments. Projection operators may also raise this exception to indicate that an object cannot be represented in the database, e.g. due to an overflow.

The above only states that intro is a left (pseudo-)inverse of the projections, which is what matters for a faithful representation of OCaml values. The opposite (projection functions being the left inverse of intro) may be relevant if the application needs preserve the database representation when updating objects.

val custom : encode:('a -> ('b, string) Stdlib.result) -> decode:('b -> ('a, string) Stdlib.result) -> 'b t -> 'a t

custom ~encode ~decode rep creates a custom type represented by rep, where encode is used to encode parameters into rep and decode is used to decode result rows from rep.

val option : 'a t -> 'a option t

option t turns a set of fields encoded as t into a correspending set of nullable fields. The encoder will encode None as into a tuple of NULL values and the decoder will return None if all fields are NULL.

If the type t itself is option t' for some t', or contains nested tuples and options such that all field types are nested under an option type, then it would have been possible to decode an all-NULL segment of a row as Some x where x is a corresponding tuple-option-tree terminating in None values. The above paragraph resolves this ambiguity since it implies that the outermost option possible will be decoded as None.

val redacted : 'a t -> 'a t

redacted t is the same type as t but sealed as potentially containing sensitive information to be redacted from pretty-printers and logs.

Tuple Types

As a common case of composite types, constructors for tuples up to 12 components are predefined here. Higher tuples can be created with product.

val unit : unit t

A type holding no fields. This is used to pass no parameters and as the result for queries which does not return any rows. It can also be nested in tuples, in which case it will not contribute to the total number of fields.

val t2 : 'a1 t -> 'a2 t -> ('a1 * 'a2) t

Creates a pair type.

val t3 : 'a1 t -> 'a2 t -> 'a3 t -> ('a1 * 'a2 * 'a3) t

Creates a 3-tuple type.

val t4 : 'a1 t -> 'a2 t -> 'a3 t -> 'a4 t -> ('a1 * 'a2 * 'a3 * 'a4) t

Creates a 4-tuple type.

val t5 : 'a1 t -> 'a2 t -> 'a3 t -> 'a4 t -> 'a5 t -> ('a1 * 'a2 * 'a3 * 'a4 * 'a5) t

Creates a 5-tuple type.

val t6 : 'a1 t -> 'a2 t -> 'a3 t -> 'a4 t -> 'a5 t -> 'a6 t -> ('a1 * 'a2 * 'a3 * 'a4 * 'a5 * 'a6) t

Creates a 6-tuple type.

val t7 : 'a1 t -> 'a2 t -> 'a3 t -> 'a4 t -> 'a5 t -> 'a6 t -> 'a7 t -> ('a1 * 'a2 * 'a3 * 'a4 * 'a5 * 'a6 * 'a7) t

Creates a 7-tuple type.

val t8 : 'a1 t -> 'a2 t -> 'a3 t -> 'a4 t -> 'a5 t -> 'a6 t -> 'a7 t -> 'a8 t -> ('a1 * 'a2 * 'a3 * 'a4 * 'a5 * 'a6 * 'a7 * 'a8) t

Creates a 8-tuple type.

val t9 : 'a1 t -> 'a2 t -> 'a3 t -> 'a4 t -> 'a5 t -> 'a6 t -> 'a7 t -> 'a8 t -> 'a9 t -> ('a1 * 'a2 * 'a3 * 'a4 * 'a5 * 'a6 * 'a7 * 'a8 * 'a9) t

Creates a 9-tuple type.

val t10 : 'a1 t -> 'a2 t -> 'a3 t -> 'a4 t -> 'a5 t -> 'a6 t -> 'a7 t -> 'a8 t -> 'a9 t -> 'a10 t -> ('a1 * 'a2 * 'a3 * 'a4 * 'a5 * 'a6 * 'a7 * 'a8 * 'a9 * 'a10) t

Creates a 10-tuple type.

val t11 : 'a1 t -> 'a2 t -> 'a3 t -> 'a4 t -> 'a5 t -> 'a6 t -> 'a7 t -> 'a8 t -> 'a9 t -> 'a10 t -> 'a11 t -> ('a1 * 'a2 * 'a3 * 'a4 * 'a5 * 'a6 * 'a7 * 'a8 * 'a9 * 'a10 * 'a11) t

Creates a 11-tuple type.

val t12 : 'a1 t -> 'a2 t -> 'a3 t -> 'a4 t -> 'a5 t -> 'a6 t -> 'a7 t -> 'a8 t -> 'a9 t -> 'a10 t -> 'a11 t -> 'a12 t -> ('a1 * 'a2 * 'a3 * 'a4 * 'a5 * 'a6 * 'a7 * 'a8 * 'a9 * 'a10 * 'a11 * 'a12) t

Creates a 12-tuple type.