custom_store

Custom Sumo Store Example

This example is about creating a store in order to add some functionality. We are going to use PostgreSQL as a backend and we want to store people (only with name and city fields).

Requirements

• PostgreSQL installed and a database created (in our code we called it store_example)

The Problem

SumoDB provides us a great bunch of functions for CRUD operations but we need a special one. We would like to have a count_by_city/1 function which returns us the number of people from a given city.

With the standard SumoDB API we could filter by city and then return the size of the array but we want to use the native power of PostgreSQL.

Creating our own store

As we are using PostgreSQL we are going to use our sumo_db_pgsql adapter for sumo, you can find it here. This Adapter provides us a store called sumo_db_pgsql which provides us the standard SumoDB API. We want to extend that module and add our custom count_by_city/1 function. In order to achive that we create our new our_pgsql_store which gets all the functionality from sumo_db_pgsql using mixer.

-mixin([sumo_store_pgsql]).

Then we can create our function:

count_by_city(City, DocName, State) ->
  #{conn := Conn} = State,
  Query = [
    "SELECT Count(city) FROM ", escape(DocName),
    " GROUP BY CITY ",
    " HAVING ",
    " city = $1"

  ],
  parse_result(epgsql:equery(Conn, stringify(Query), [City]), State).

We are using epgsql directly from here because it is the driver we are using in the adapter. Don't worry about escape/1, stringify/1 and parse_result/1, you can check the real code in the source.

Now we have to use this new store on our config file.

Calling to our new function

We have added the function to our store but now we have to call that function integrated with SumoDB, we are going to create a new function in store_example module:

count_by_city(City) ->
  sumo:call(people, count_by_city, [City]).

This is how we call directly to a store. The first parameter is the model (defined in the config), the second one is the name of the store's function (our new created function) and the last one is a list with the parameters the that new function, in this case only one parameter.

and thats all!

Running the example

• First clone the code to your local system.
• You must create a new database in PostgreSQL.
• Review the config/sys.config info about your database, by default the database configuration is:

{host,     "127.0.0.1"},
{port,      5432},
{database, "store_example"},
{username, "ferigis"},
{password, "123456"}

replace what you need

• Compile the code

rebar3 compile

• Run

erl -pa _build/default/lib/*/ebin -config config/sys.config -s store_example

Play!

Lets create some people:

2> sumo:persist(people, person:new("Felipe", "San Jose")).
#{city => "San Jose",id => 1,name => "Felipe"}
3> sumo:persist(people, person:new("Carlos", "Cali")).
#{city => "Cali",id => 2,name => "Carlos"}
4> sumo:persist(people, person:new("Brujo", "Buenos Aires")).
#{city => "Buenos Aires",id => 3,name => "Brujo"}
5> sumo:persist(people, person:new("Marcos", "Buenos Aires")).
#{city => "Buenos Aires",id => 4,name => "Marcos"}
6> sumo:persist(people, person:new("Euen", "Buenos Aires")).
#{city => "Buenos Aires",id => 5,name => "Euen"}

Lets find one of them (here we are checking we have extended from the default PostgreSQL store correctly):

7> sumo:find_by(people, [{name, "Brujo"}]).
[#{city => <<"Buenos Aires">>,id => 3,name => <<"Brujo">>}]

Great!

Now lets use our new function:

8> store_example:count_by_city("Buenos Aires").
3
9> store_example:count_by_city("San Jose").
1
10> store_example:count_by_city("Cali").
1
11> store_example:count_by_city("Namek").
0

It worked!

This is the idea behind creating your own store