为 Hasql 查询编码参数列表

Question

我正在尝试获取 Hasql to encode a list for a "select ... where in" query. It typechecks if I use contramany from contravariant-extras，但在运行时出现语法错误。

import qualified Database.Encoders as E
import Contravariant.Extras

getTeamMembership :: Query [TeamId] [(TeamId, EmployeeId)]
getTeamMembership = statement q enc def True
  where
    enc = contramany (E.value E.teamId)
    q = "select workteam, employee \
        \from workteam_employee where workteam in "

是否不能对参数列表进行编码？

Answer 1

"IN" 运算符不支持。您只能用它指定单个值（例如，IN (, , )）。然而，根据 the docs.

，使用数组编码器和 any 和 all Postgres 函数可以轻松实现您想要的。

有some Hasql tests showing it in action.

问题跟踪器上也有 a discussion on that subject。

为 Hasql 查询编码参数列表

Encoding a Parameter List for a Hasql query

postgresql

haskell

contravariance

hasql