Stack Overflow
Stack Overflow

Questions tagged [haskell-persistent]

Persistent is a type-safe, universal data store interface for Haskell with support for various backends, including PostgreSQL, SQLite, MySQL and MongoDB.

57 questions
2
votes
2 answers

In Persistent (Haskell), how can I insert a record only if it doesn't already exist?

I'm a Haskell beginner, so apologies in advance! I've been following the Persistent tutorial here. I have a data model with a uniqueness constraint: Book gutId Int UniqueGutId gutId ... author [AuthorId] ... Author gutId…
Jonathan
  • 10,571
  • 13
  • 67
  • 103
2
votes
1 answer

How can I use a field from my Persistent model as a path piece in my routes file?

I have a Persistent model like so: Organization sql=organizations Id UUID default=uuid_generate_v1mc name Text UniqueOrganizationName name deriving Show Eq Typeable I'd like to use the organization name in my Yesod routes file like…
MaxGabriel
  • 7,617
  • 4
  • 35
  • 82
2
votes
1 answer

How does "import Database.Persist as X hiding (get)" from the yesod-sqlite template works

I am using the yesod-sqlite template and trying to use the get function from Database.Persist in a test. Here is my code: [Entity _ task] <- runDB $ selectList [TaskName ==. name] [] ... user <- runDB $ X.get (taskUserId task) And the error I am…
Fábio Roberto Teodoro
  • 499
  • 1
  • 6
  • 17
2
votes
2 answers

Inner join in persistent or should I use esqueleto?

I have this fragment describing Notification and Notified entities: Notification type NotiType release ReleaseId date UTCTime Notified aboutWhat NotificationId unread Bool user UserId Now I…
Mark Karpov
  • 7,499
  • 2
  • 27
  • 62
2
votes
0 answers

Is there a tool for generating Persistent entity definitions from an existing database?

I understand you can use persistent-template to declare entities, but is there a tool for building those from an existing database? Specifically is there a tool that can be pointed at a MySQL database and return definitions that can be used by…
ryantm
  • 8,217
  • 6
  • 45
  • 57
1
vote
0 answers

How can I generate the list of `EntityField`s for a `PersistEntity`?

I was trying to implement some form of repsertBy: repsert where the key is a provided Unique, in the line of getBy, upsertBy etc. My approach: implement it on top of upsertBy. Now upsertBy takes a unique constraint, a record, and a list of changes…
JB.
  • 40,344
  • 12
  • 79
  • 106
1
vote
1 answer

How do I pass a rendered persistent/esqueleto query to another query?

I'd like to use Persistent/Esqueleto to implement count estimates. One approach recommended in this article is to define a function like this CREATE FUNCTION count_estimate(query text) RETURNS integer AS $$ DECLARE rec record; rows …
Jezen Thomas
  • 13,619
  • 6
  • 53
  • 91
1
vote
1 answer

Haskell + Persistent: parse error possibly incorrect indentation or mismatched brackets

I have been learning Haskell for the last several months and am trying to follow along with this tutorial on Haskell + Persistent: https://www.yesodweb.com/book/persistent#persistent_code_generation module Main where {-# LANGUAGE GADTs …
Will Taylor
  • 1,650
  • 9
  • 23
1
vote
2 answers

What is the strategy for working with different types of Monad Transformers?

I'm trying to implement a simple web server that interacts with some other API and stores the response after doing some processing. To encapsulate the possibility of failure (empty response, incorrect request, etc) I am using ExceptT as…
atis
  • 881
  • 5
  • 22
1
vote
0 answers

Copying data between databases using Haskell Persistent

First up, I have a large Sqlite database. I want to copy a subset of the data in this database to another Sqlite database in a streaming fashion using the Haskell persistent library. Here's the only I managed to do it, but its very slow (and uses…
kolam
  • 731
  • 4
  • 17
1
vote
2 answers

Haskell and postgresql - build error "The program pg_config is required but it could not be found."

I am currently learning haskell and just tried using postgresql as a database. I generated my project with stack (stack new -> stack setup -> stack build) and then all I changed was adding the dependencies needed to persistent and postgresql…
B16
  • 50
  • 1
  • 7
1
vote
1 answer

Inserting entry into database using PostGreSQL & Persistent

I'm trying to learn the Persistent Library. I have two files one with all the types I've defined for my project (diet tracker) Report.hs data FoodEntry = FoodEntry { report :: Report , date :: UTCTime …
distro.obs
  • 181
  • 9
1
vote
1 answer

How to get referenced model information in Yesod?

I have 3 Models Address json number Text street Text pincode Text deriving Show Person json email Text name Text telephone Text deriving Show House json rent Int ownerId PersonId addressId AddressId …
Sumanth Kumar Mora
  • 637
  • 1
  • 5
  • 15
1
vote
2 answers

Yesod return whole Entity after insert?

Basically right now I run fbId <- runDB $ insert myNewFooBar and I get back a Key FooBar. Is there any way to return the value of the whole FooBar directly from an insert without running a separate query of runDB $ get404 fbId after?
BWStearns
  • 2,567
  • 2
  • 19
  • 33
1
vote
1 answer

Haskell Esqueleto 3 table join

These are my attempts to do a SELECT from three tables. But they don't compile and I don't understand the error (I don't know why it expects a tuple (Entity Issue, b0) instead of the triplet I think the code attempts to get). Attempt 1: {-# LANGUAGE…
hhefesto
  • 331
  • 1
  • 11
1
2
3 4