1
0
mirror of https://github.com/hasura/graphql-engine.git synced 2024-12-20 22:11:45 +03:00
graphql-engine/server/src-lib/Hasura/Backends/MSSQL/FromIr.hs

Ignoring revisions in .git-blame-ignore-revs. Click here to bypass and see the normal blame view.

98 lines
3.4 KiB
Haskell
Raw Normal View History

-- | The modules in the @Hasura.Backends.MSSQL.FromIr@ namespace translates the
-- RQL IR into TSQL, the SQL dialect of MSSQL, as defined in abstract syntax in
-- "Hasura.Backends.MSSQL.Types".
--
-- The translation happens in the @FromIr@ monad, which manages identifier
-- scoping and error collection.
--
-- The actual rendering of this AST into TSQL text happens in
-- "Hasura.Backends.MSSQL.ToQuery".
module Hasura.Backends.MSSQL.FromIr
( -- * The central Monad
FromIr,
runFromIr,
Error (..),
-- * Name generation
NameTemplate (..),
generateAlias,
)
where
import Control.Monad.Validate
import Control.Monad.Validate qualified as V
import Data.Map.Strict (Map)
import Data.Map.Strict qualified as M
import Data.Text qualified as T
import Hasura.Backends.MSSQL.Instances.Types ()
import Hasura.Backends.MSSQL.Types.Internal as TSQL
import Hasura.Base.Error (QErr, throw500)
import Hasura.Prelude
server: support remote relationships on SQL Server and BigQuery (#1497) Remote relationships are now supported on SQL Server and BigQuery. The major change though is the re-architecture of remote join execution logic. Prior to this PR, each backend is responsible for processing the remote relationships that are part of their AST. This is not ideal as there is nothing specific about a remote join's execution that ties it to a backend. The only backend specific part is whether or not the specification of the remote relationship is valid (i.e, we'll need to validate whether the scalars are compatible). The approach now changes to this: 1. Before delegating the AST to the backend, we traverse the AST, collect all the remote joins while modifying the AST to add necessary join fields where needed. 1. Once the remote joins are collected from the AST, the database call is made to fetch the response. The necessary data for the remote join(s) is collected from the database's response and one or more remote schema calls are constructed as necessary. 1. The remote schema calls are then executed and the data from the database and from the remote schemas is joined to produce the final response. ### Known issues 1. Ideally the traversal of the IR to collect remote joins should return an AST which does not include remote join fields. This operation can be type safe but isn't taken up as part of the PR. 1. There is a lot of code duplication between `Transport/HTTP.hs` and `Transport/Websocket.hs` which needs to be fixed ASAP. This too hasn't been taken up by this PR. 1. The type which represents the execution plan is only modified to handle our current remote joins and as such it will have to be changed to accommodate general remote joins. 1. Use of lenses would have reduced the boilerplate code to collect remote joins from the base AST. 1. The current remote join logic assumes that the join columns of a remote relationship appear with their names in the database response. This however is incorrect as they could be aliased. This can be taken up by anyone, I've left a comment in the code. ### Notes to the reviewers I think it is best reviewed commit by commit. 1. The first one is very straight forward. 1. The second one refactors the remote join execution logic but other than moving things around, it doesn't change the user facing functionality. This moves Postgres specific parts to `Backends/Postgres` module from `Execute`. Some IR related code to `Hasura.RQL.IR` module. Simplifies various type class function signatures as a backend doesn't have to handle remote joins anymore 1. The third one fixes partial case matches that for some weird reason weren't shown as warnings before this refactor 1. The fourth one generalizes the validation logic of remote relationships and implements `scalarTypeGraphQLName` function on SQL Server and BigQuery which is used by the validation logic. This enables remote relationships on BigQuery and SQL Server. https://github.com/hasura/graphql-engine-mono/pull/1497 GitOrigin-RevId: 77dd8eed326602b16e9a8496f52f46d22b795598
2021-06-11 06:26:50 +03:00
import Hasura.RQL.IR qualified as IR
import Hasura.SQL.Backend
-- | The central Monad used throughout for all conversion functions.
--
-- It has the following features:
--
-- * It's a 'MonadValidate', so it'll continue going when it encounters 'Error's
-- to accumulate as many as possible.
--
-- * It has a facility for generating fresh, unique aliases, which lets the
-- translation output retain a resemblance with source names without the
-- translation process needing to be bothered about potential name shadowing.
-- See 'generateAlias'.
newtype FromIr a = FromIr
{ unFromIr :: StateT (Map Text Int) (Validate (NonEmpty Error)) a
}
deriving (Functor, Applicative, Monad, MonadValidate (NonEmpty Error))
-- | Run a 'FromIr' action, throwing errors that have been collected using the
-- supplied action.
runFromIr :: MonadError QErr m => FromIr a -> m a
runFromIr = flip onLeft (throw500 . tshow) . V.runValidate . flip evalStateT mempty . unFromIr
-- | Errors that may happen during translation.
data Error
= UnsupportedOpExpG (IR.OpExpG 'MSSQL Expression)
| FunctionNotSupported
deriving (Show, Eq)
-- | Hints about the type of entity that 'generateAlias' is producing an alias
-- for.
data NameTemplate
= ArrayRelationTemplate Text
| ArrayAggregateTemplate Text
| ObjectRelationTemplate Text
| TableTemplate Text
| ForOrderAlias Text
-- | Generate a fresh alias for a given entity to remove ambiguity and naming
-- conflicts between scopes at the TSQL level.
--
-- Names are generated in the form @type_name_occurrence@, where:
--
-- * @type@ hints at the type of entity,
-- * @name@ refers to the source name being aliased, and
-- * @occurrence@ is an integer counter that distinguishes each occurrence of @type_name@.
--
-- Example outputs:
--
-- > do
-- > "ar_articles_1" <- generateAlias (ArrayRelationTemplate "articles")
-- > "ar_articles_2" <- generateAlias (ArrayRelationTemplate "articles")
-- > "t_users_1" <- generateAlias (TableTemplate "users")
generateAlias :: NameTemplate -> FromIr Text
generateAlias template = do
FromIr (modify' (M.insertWith (+) rendered 1))
occurrence <- M.findWithDefault 1 rendered <$> FromIr get
pure (rendered <> tshow occurrence)
where
rendered = T.take 20 $
case template of
ArrayRelationTemplate sample -> "ar_" <> sample
ArrayAggregateTemplate sample -> "aa_" <> sample
ObjectRelationTemplate sample -> "or_" <> sample
TableTemplate sample -> "t_" <> sample
ForOrderAlias sample -> "order_" <> sample