Provide table name at runtime when building relations #57

bssstudio · 2018-02-21T23:38:07Z

Hi!
In my use case, I have multiple tables with schema that is exactly the same. What I would like to do is to provide the table name at runtime. I would use one table to generate the definitions with template haskell, but when building a relation, I would provide a different name.

nRel :: String -> Relation () MyData
nRel name = relationName name $ do
  query $ MyData.myData
  ...

Is this currently possible, or might this be a feature request?

The text was updated successfully, but these errors were encountered:

igrep · 2018-03-20T08:01:36Z

Providing a table name as a String can break the type safety of this library.
So you should not do that.

I have multiple tables with schema that is exactly the same.

I guess you should make use of HasProjection type class.
Given tables with columns foo :: String and bar :: Int, you can write the query like this.

(Updated due to a type error)

nRel
  :: (HasProjection "foo" a String, HasProjection "bar" a Int)
  => Relation () a -> Relation () a
nRel tbl = relation $ do
  t <- query tbl
  wheres $ t ! #bar .=. value "some bar value"
  ...

(You may have to enable DataKinds, OverloadedLabels, and the other related extensions).

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Provide table name at runtime when building relations #57

Provide table name at runtime when building relations #57

bssstudio commented Feb 21, 2018 •

edited

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igrep commented Mar 20, 2018 •

edited

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Provide table name at runtime when building relations #57

Provide table name at runtime when building relations #57

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bssstudio commented Feb 21, 2018 • edited Loading

igrep commented Mar 20, 2018 • edited Loading

bssstudio commented Feb 21, 2018 •

edited

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igrep commented Mar 20, 2018 •

edited

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