Walkable supports SQL pagination you've been familiar with: OFFSET, LIMIT and ORDER BY.

Inside a query's parameters

You can specify how to paginate your query by providing any combination of pagination keywords, namely: :offset, :limit, :order-by.

• No pagination:

  Query

  SQL output

  `[{(:farmers/all {})
     [:farmer/number :farmer/name]}]]
  ;; the same as:
  `[{:farmers/all
     [:farmer/number :farmer/name]}]]
  

  SELECT farmer.number, farmer.name FROM farmer
  

• Pagination with :limit and :order-by:

  Query

  SQL output

  `[{(:farmers/all {:limit 3 :order-by :farmer/number})
     [:farmer/number :farmer/name]}]]
  

  SELECT farmer.number, farmer.name
   FROM farmer
   LIMIT 3
   ORDER BY farmer.number
  

• Who says :order-by has to be simple?

  Query

  SQL output

  `[{(:farmers/all {:order-by [:farmer/number :farmer/name :desc :nils-first]})
     [:farmer/number :farmer/name]}]]
  

  SELECT farmer.number, farmer.name
  FROM farmer
  ORDER BY farmer.number, farmer.name DESC NULLS FIRST
  

Validator and default value

Pagination can be a bomb if you let client apps specify whatever parameters. You can just tell Walkable how pagination parameters must comply and default values when provided parameters fail that (or not even provided at all).

Validators and respective default values can be declared for each idents it in :floor-plan.

Offset and limit

For :offset and :limit, value of :default must be a number while :validate is a function that check if the supplied parameter satisfies your constraint.

{:idents
 {:farmers/all "farmer"}

 :pagination-fallbacks
 {:farmers/all
  {:offset {:default  2
            :validate #(<= 0 % 100)}}}}

`[{(:farmers/all {:offset 9999})
   [:farmer/number :farmer/name]}]]

SELECT farmer.number, farmer.name
FROM farmer
OFFSET 2

Order-by

For :order-by, value of :default must be a valid order-by expression while :validate is a function that check if all the supplied columns satisfies your constraint. Usually you want a simple set for your validator.

{:idents
 {:farmers/all "farmer"}

 :pagination-fallbacks
 {:farmers/all
  {:order-by {:default  [:farmer/number :asc]
              :validate #{:farmer/number :farmer/yob}}}}}

`[{(:farmers/all {:order-by [:farmer/number :desc :farmer/yob :nils-first]})
   [:farmer/number :farmer/name]}]]

SELECT farmer.number, farmer.name
FROM farmer
ORDER BY farmer.number DESC, farmer.yob NULLS FIRST

{:idents
 {:farmers/all "farmer"}

 :pagination-fallbacks
 {:farmers/all
  {:order-by {:default  [:farmer/number :asc]
              :validate #{:farmer/number :farmer/yob}}}}}

`[{(:farmers/all {:order-by [:farmer/number :desc :farmer/name :nils-first]})
   [:farmer/number :farmer/name]}]]

SELECT farmer.number, farmer.name
FROM farmer
ORDER BY farmer.number ASC