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  1. fromStartMaybe :: (PersistEntity a, BackendCompatible SqlBackend (PersistEntityBackend a)) => SqlQuery (PreprocessedFrom (SqlExpr (Maybe (Entity a))))

    esqueleto Database.Esqueleto.Internal.Internal

    (Internal) Same as fromStart, but entity may be missing.

  2. subSelectMaybe :: PersistField a => SqlQuery (SqlExpr (Value (Maybe a))) -> SqlExpr (Value (Maybe a))

    esqueleto Database.Esqueleto.Internal.Internal

    Execute a subquery SELECT in a SqlExpr. This function is a shorthand for the common joinV . subSelect idiom, where you are calling subSelect on an expression that would be Maybe already. As an example, you would use this function when calling sum_ or max_, which have Maybe in the result type (for a 0 row query).

  3. toBaseIdMaybe :: ToBaseId ent => SqlExpr (Value (Maybe (Key ent))) -> SqlExpr (Value (Maybe (Key (BaseEnt ent))))

    esqueleto Database.Esqueleto.Internal.Internal

    Like toBaseId, but works on Maybe keys.

  4. ByMaybeAttr :: WhyNullable

    esqueleto Database.Esqueleto.Legacy

    No documentation available.

  5. FieldAttrMaybe :: FieldAttr

    esqueleto Database.Esqueleto.Legacy

    The Maybe keyword goes after the type. This indicates that the column is nullable, and the generated Haskell code will have a Maybe type for it. Example: 

    User
name Text Maybe

  6. fromBaseIdMaybe :: ToBaseId ent => SqlExpr (Value (Maybe (Key (BaseEnt ent)))) -> SqlExpr (Value (Maybe (Key ent)))

    esqueleto Database.Esqueleto.Legacy

    As fromBaseId, but works on Maybe keys.

  7. isFieldMaybe :: FieldDef -> Bool

    esqueleto Database.Esqueleto.Legacy

    Check if the field is `Maybe a`

  8. subSelectMaybe :: PersistField a => SqlQuery (SqlExpr (Value (Maybe a))) -> SqlExpr (Value (Maybe a))

    esqueleto Database.Esqueleto.Legacy

    Execute a subquery SELECT in a SqlExpr. This function is a shorthand for the common joinV . subSelect idiom, where you are calling subSelect on an expression that would be Maybe already. As an example, you would use this function when calling sum_ or max_, which have Maybe in the result type (for a 0 row query).

  9. toBaseIdMaybe :: ToBaseId ent => SqlExpr (Value (Maybe (Key ent))) -> SqlExpr (Value (Maybe (Key (BaseEnt ent))))

    esqueleto Database.Esqueleto.Legacy

    Like toBaseId, but works on Maybe keys.

  10. upsertMaybe :: forall (m :: Type -> Type) record . (MonadIO m, PersistEntity record, OnlyOneUniqueKey record, PersistRecordBackend record SqlBackend, IsPersistBackend (PersistEntityBackend record)) => record -> [SqlExpr (Entity record) -> SqlExpr Update] -> ReaderT SqlBackend m (Maybe (Entity record))

    esqueleto Database.Esqueleto.PostgreSQL

    Like upsert, but permits an empty list of updates to be performed. If no updates are provided and the record already was present in the database, then this will return Nothing. If you want to fetch the record out of the database, you can write: 

    mresult <- upsertMaybe record []
case mresult of
Nothing ->
getBy (onlyUniqueP record)
Just res ->
pure (Just res)

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