package query
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Type Members
- trait Cache extends AnyRef
A
Cache
maintains an internal state with a mapping from requests toRef
s that will contain the result of those requests when they are executed.A
Cache
maintains an internal state with a mapping from requests toRef
s that will contain the result of those requests when they are executed. This is used internally by the library to provide deduplication and caching of requests. - final class CompletedRequestMap extends AnyRef
A
CompletedRequestMap
is a universally quantified mapping from requests of typeRequest[E, A]
to results of typeEither[E, A[
for all typesE
andA
.A
CompletedRequestMap
is a universally quantified mapping from requests of typeRequest[E, A]
to results of typeEither[E, A[
for all typesE
andA
. The guarantee is that for any request of typeRequest[E, A]
, if there is a corresponding value in the map, that value is of typeEither[E, A]
. This is used by the library to support data sources that return different result types for different requests while guaranteeing that results will be of the type requested. - trait DataSource[-R, -A] extends AnyRef
A
DataSource[R, A]
requires an environmentR
and is capable of executing requests of typeA
.A
DataSource[R, A]
requires an environmentR
and is capable of executing requests of typeA
.Data sources must implement the method
runAll
which takes a collection of requests and returns an effect with aCompletedRequestMap
containing a mapping from requests to results. The type of the collection of requests is aChunk[Chunk[A]]
. The outerChunk
represents batches of requests that must be performed sequentially. The innerChunk
represents a batch of requests that can be performed in parallel. This allows data sources to introspect on all the requests being executed and optimize the query.Data sources will typically be parameterized on a subtype of
Request[A]
, though that is not strictly necessarily as long as the data source can map the request type to aRequest[A]
. Data sources can then pattern match on the collection of requests to determine the information requested, execute the query, and place the results into theCompletedRequestsMap
using CompletedRequestMap.empty and CompletedRequestMap.insert. Data sources must provide results for all requests received. Failure to do so will cause a query to die with aQueryFailure
when run. - trait DataSourceAspect[-R] extends AnyRef
A
DataSourceAspect
is an aspect that can be weaved into queries.A
DataSourceAspect
is an aspect that can be weaved into queries. You can think of an aspect as a polymorphic function, capable of transforming one data source into another, possibly enlarging the environment type. - final case class Described[+A](value: A, description: String) extends Product with Serializable
A
Described[A]
is a value of typeA
along with a string description of that value.A
Described[A]
is a value of typeA
along with a string description of that value. The description may be used to generate a hash associated with the value, so values that are equal should have the same description and values that are not equal should have different descriptions. - type Query[+E, +A] = ZQuery[Any, E, A]
- final case class QueryFailure(dataSource: DataSource[Nothing, Nothing], request: Request[Any, Any]) extends Throwable with Product with Serializable
QueryFailure
keeps track of details relevant to query failures. - type RQuery[-R, +A] = ZQuery[R, Throwable, A]
- trait Request[+E, +A] extends AnyRef
A
Request[E, A]
is a request from a data source for a value of typeA
that may fail with anE
.A
Request[E, A]
is a request from a data source for a value of typeA
that may fail with anE
.sealed trait UserRequest[+A] extends Request[Nothing, A] case object GetAllIds extends UserRequest[List[Int]] final case class GetNameById(id: Int) extends UserRequest[String]
- type TaskQuery[+A] = ZQuery[Any, Throwable, A]
- type UQuery[+A] = ZQuery[Any, Nothing, A]
- type URQuery[-R, +A] = ZQuery[R, Nothing, A]
- final class ZQuery[-R, +E, +A] extends AnyRef
A
ZQuery[R, E, A]
is a purely functional description of an effectual query that may contain requests from one or more data sources, requires an environmentR
, and may fail with anE
or succeed with anA
.A
ZQuery[R, E, A]
is a purely functional description of an effectual query that may contain requests from one or more data sources, requires an environmentR
, and may fail with anE
or succeed with anA
.Requests that can be performed in parallel, as expressed by
zipWithPar
and combinators derived from it, will automatically be batched. Requests that must be performed sequentially, as expressed byzipWith
and combinators derived from it, will automatically be pipelined. This allows for aggressive data source specific optimizations. Requests can also be deduplicated and cached.This allows for writing queries in a high level, compositional style, with confidence that they will automatically be optimized. For example, consider the following query from a user service.
val getAllUserIds: ZQuery[Any, Nothing, List[Int]] = ??? def getUserNameById(id: Int): ZQuery[Any, Nothing, String] = ??? for { userIds <- getAllUserIds userNames <- ZQuery.foreachPar(userIds)(getUserNameById) } yield userNames
This would normally require N + 1 queries, one for
getAllUserIds
and one for each call togetUserNameById
. In contrast,ZQuery
will automatically optimize this to two queries, one foruserIds
and one foruserNames
, assuming an implementation of the user service that supports batching.Based on "There is no Fork: an Abstraction for Efficient, Concurrent, and Concise Data Access" by Simon Marlow, Louis Brandy, Jonathan Coens, and Jon Purdy. http://simonmar.github.io/bib/papers/haxl-icfp14.pdf
Value Members
- object Cache
- object CompletedRequestMap
- object DataSource
- object DataSourceAspect
- object Described extends Serializable
- object ZQuery