Adding our First Commands
=========================

Now that we have everything set up and we know how commands are implemented it's
time to implement our own.

To start we are going to implement a simple in memory key value store, the
first two commands we are going to implement are the basic ones we need to see
if it works: put and get

To hold the values we are going to use the `Erlang Term Storage (ETS) <http://www.erlang.org/doc/man/ets.html>`_.

Riak Core API
-------------

First we start by `creating the two new metrics <https://github.com/marianoguerra/tanodb/commit/398e3ae0a6ede7529aa1fee3930640c9598a45df#diff-afa3f67ec87f742d64ee9ed311455777R4>`_ for our new commands.

Then we add the commands to tanodb.erl, `get <https://github.com/marianoguerra/tanodb/commit/398e3ae0a6ede7529aa1fee3930640c9598a45df#diff-6f7251bf9e224ebabd766f0331b848adR15>`_ and
`put <https://github.com/marianoguerra/tanodb/commit/398e3ae0a6ede7529aa1fee3930640c9598a45df#diff-6f7251bf9e224ebabd766f0331b848adR19>`_ we extract the common code to hash
the key to a vnode to a private function called `send_to_one <https://github.com/marianoguerra/tanodb/commit/398e3ae0a6ede7529aa1fee3930640c9598a45df#diff-6f7251bf9e224ebabd766f0331b848adR25>`_.

On the riak_core side, that is, in the tanodb_vnode module, on init `we create
our ETS table <https://github.com/marianoguerra/tanodb/commit/398e3ae0a6ede7529aa1fee3930640c9598a45df#diff-942e4ef944df628266f096d2fbcd4348R30>`_, the name is tanodb_<partition> where <partition> is the partition id.

Then we `add two new function clauses to handle_command <https://github.com/marianoguerra/tanodb/commit/398e3ae0a6ede7529aa1fee3930640c9598a45df#diff-942e4ef944df628266f096d2fbcd4348R41>`_, one for put and one for get. The logic is quite simple.

The code from tanodb.erl:

.. code-block:: erlang

    get(Key) ->
        tanodb_metrics:core_get(),
        send_to_one(Key, {get, Key}).

    delete(Key) ->
        tanodb_metrics:core_delete(),
        send_to_one(Key, {delete, Key}).

    put(Key, Value) ->
        tanodb_metrics:core_put(),
        send_to_one(Key, {put, Key, Value}).

    % private functions

    send_to_one(Key, Cmd) ->
        DocIdx = riak_core_util:chash_key(Key),
        PrefList = riak_core_apl:get_primary_apl(DocIdx, 1, tanodb),
        [{IndexNode, _Type}] = PrefList,
        riak_core_vnode_master:sync_spawn_command(IndexNode, Cmd,
             tanodb_vnode_master).

The relevant code from tanodb_vnode.erl:

.. code-block:: erlang

    handle_command({put, Key, Value}, _Sender,
                   State=#state{table_name=TableName, partition=Partition}) ->
        ets:insert(TableName, {Key, Value}),
        {reply, {ok, Partition}, State};

    handle_command({get, Key}, _Sender,
                   State=#state{table_name=TableName, partition=Partition}) ->
        case ets:lookup(TableName, Key) of
            [] ->
                {reply, {not_found, Partition, Key}, State};
            [Value] ->
                {reply, {found, Partition, {Key, Value}}, State}
        end;

    handle_command({delete, Key}, _Sender,
                   State=#state{table_name=TableName, partition=Partition}) ->
        case ets:lookup(TableName, Key) of
            [] ->
                {reply, {not_found, Partition, Key}, State};
            [Value] ->
                true = ets:delete(TableName, Key),
                {reply, {found, Partition, {Key, Value}}, State}
        end;

Test it
.......

Stop, build, start and in the console we run some commands.

First try getting the key "k1" from bucket "mybucket", which doesn't exist:

.. code-block:: erlang

    (tanodb@127.0.0.1)2> tanodb:get({<<"mybucket">>, <<"k1">>}).

    {not_found,228359630832953580969325755111919221821239459840,
               {<<"mybucket">>,<<"k1">>}}

We get not_found back with the partition that handled the command and the bucket
and key that wasn't found.

Now let's put that key:

.. code-block:: erlang

    (tanodb@127.0.0.1)3> tanodb:put({<<"mybucket">>, <<"k1">>}, 42).

    {ok,228359630832953580969325755111919221821239459840}

We just get ok back, let's try to get it again:

.. code-block:: erlang

    (tanodb@127.0.0.1)4> tanodb:get({<<"mybucket">>, <<"k1">>}).

    {found,228359630832953580969325755111919221821239459840,
           {{<<"mybucket">>,<<"k1">>},{{<<"mybucket">>,<<"k1">>},42}}}

Now we get the value back.

Let's try the same with another key:

.. code-block:: erlang

    (tanodb@127.0.0.1)5> tanodb:get({<<"mybucket">>, <<"k2">>}).

    {not_found,1210306043414653979137426502093171875652569137152,
               {<<"mybucket">>,<<"k2">>}}

Notice that the partition id changed, this is because the key hashed to a different
vnode.

.. code-block:: erlang

    (tanodb@127.0.0.1)6> tanodb:put({<<"mybucket">>, <<"k2">>}, 42).

    {ok,1210306043414653979137426502093171875652569137152}

.. code-block:: erlang

    (tanodb@127.0.0.1)7> tanodb:get({<<"mybucket">>, <<"k2">>}).

    {found,1210306043414653979137426502093171875652569137152,
           {{<<"mybucket">>,<<"k2">>},{{<<"mybucket">>,<<"k2">>},42}}}


REST API
--------

Let's expose our new functions as a REST API, first we `add a new route to
cowboy for our store <https://github.com/marianoguerra/tanodb/commit/88afaad754db69b1c8967e2fe6e4625aab6fe6aa#diff-4477d4dd0aa2db0e274a56c9158207bdR74>`_, the API will be like this:

* POST /store/:bucket/:key <json-body>: stores <json-body> under {:bucket, :key}

  + returns 204 No Content on success

* GET /store/:bucket/:key: 

  + returns 404 if :key doesn't exist on :bucket
  + returns 200 and the value stored under {:bucket, :key} if found

The implementation of the store api is quite simple if you know cowboy, it's
in the `tanodb_http_store.erl file <https://github.com/marianoguerra/tanodb/blob/88afaad754db69b1c8967e2fe6e4625aab6fe6aa/apps/tanodb/src/tanodb_http_store.erl>`_.

Test it
.......

Do the usual stop, build, run and then from another shell:

.. code-block:: sh

    $ http localhost:8080/store/mybucket/bob

Returns

.. code-block:: http

    HTTP/1.1 404 Not Found
    content-length: 0
    content-type: application/json
    date: Fri, 30 Oct 2015 17:16:16 GMT
    server: Cowboy

Let's put something on that bucket/key:

.. code-block:: sh

    $ http post localhost:8080/store/mybucket/bob name=bob color=yellow

.. code-block:: http

    HTTP/1.1 204 No Content
    content-length: 0
    content-type: application/json
    date: Fri, 30 Oct 2015 17:17:25 GMT
    server: Cowboy

And try to get it again:

.. code-block:: sh

    $ http localhost:8080/store/mybucket/bob

.. code-block:: http

    HTTP/1.1 200 OK
    content-length: 31
    content-type: application/json
    date: Fri, 30 Oct 2015 17:18:06 GMT
    server: Cowboy

    {
        "color": "yellow",
        "name": "bob"
    }

Implementing Delete
-------------------

Let's implement the delete command and REST API so our API is complete.

We start as usual `adding the metrics for the delete command <https://github.com/marianoguerra/tanodb/commit/735058ec0c00f1045682982f527cfe0a70a21537#diff-afa3f67ec87f742d64ee9ed311455777R4>`_, then `add the delete function on the tanodb module <https://github.com/marianoguerra/tanodb/commit/735058ec0c00f1045682982f527cfe0a70a21537#diff-6f7251bf9e224ebabd766f0331b848adR19>`_ which is really similar to get.

After that we `add the new function clause in handle_command in our vnode <https://github.com/marianoguerra/tanodb/commit/735058ec0c00f1045682982f527cfe0a70a21537#diff-942e4ef944df628266f096d2fbcd4348R53>`_, notice that it returns the same values as get, this is to get
back the last value in case it was found or inform us that there wasn't a value
with that bucket and key.

Finally we `handle the DELETE HTTP method in our cowboy handler <https://github.com/marianoguerra/tanodb/commit/735058ec0c00f1045682982f527cfe0a70a21537#diff-49cafd1f97d6013b2a41319db4c7961fR36>`_.

Test it
.......

Let's start by testing the core API, we get a key that is not there:

.. code-block:: erlang

    (tanodb@127.0.0.1)1> tanodb:get({<<"mybucket">>, <<"k1">>}).

    {not_found,228359630832953580969325755111919221821239459840,
               {<<"mybucket">>,<<"k1">>}}

Then set it to the value 42:

.. code-block:: erlang

    (tanodb@127.0.0.1)2> tanodb:put({<<"mybucket">>, <<"k1">>}, 42).

    {ok,228359630832953580969325755111919221821239459840}

Get it to make sure it's there:

.. code-block:: erlang

    (tanodb@127.0.0.1)3> tanodb:get({<<"mybucket">>, <<"k1">>}).

    {found,228359630832953580969325755111919221821239459840,
           {{<<"mybucket">>,<<"k1">>},{{<<"mybucket">>,<<"k1">>},42}}}

Proceed to delete it, notice that it returns the last seen value and the
result has the same shape as a get call:

.. code-block:: erlang

    (tanodb@127.0.0.1)4> tanodb:delete({<<"mybucket">>, <<"k1">>}).

    {found,228359630832953580969325755111919221821239459840,
           {{<<"mybucket">>,<<"k1">>},{{<<"mybucket">>,<<"k1">>},42}}}

We get it again to make sure it was deleted:

.. code-block:: erlang

    (tanodb@127.0.0.1)5> tanodb:get({<<"mybucket">>, <<"k1">>}).

    {not_found,228359630832953580969325755111919221821239459840,
               {<<"mybucket">>,<<"k1">>}}

And try to delete it again to see how it handles trying to delete a key that
is not there:

.. code-block:: erlang

    (tanodb@127.0.0.1)6> tanodb:delete({<<"mybucket">>, <<"k1">>}).

    {not_found,228359630832953580969325755111919221821239459840,
               {<<"mybucket">>,<<"k1">>}}

Now that we checked it works on the Erlang shell, let's try the REST API, we
will do the same as before, first get and expect not found:

.. code-block:: sh

    $ http localhost:8080/store/mybucket/bob

    HTTP/1.1 404 Not Found
    content-length: 0
    content-type: application/json
    date: Fri, 30 Oct 2015 17:32:17 GMT
    server: Cowboy

Then POST a value:

.. code-block:: sh

    $ http post localhost:8080/store/mybucket/bob name=bob color=yellow

.. code-block:: http

    HTTP/1.1 204 No Content
    content-length: 0
    content-type: application/json
    date: Fri, 30 Oct 2015 17:32:21 GMT
    server: Cowboy

GET it to make sure it's there:

.. code-block:: sh

    $ http localhost:8080/store/mybucket/bob

.. code-block:: http

    HTTP/1.1 200 OK
    content-length: 31
    content-type: application/json
    date: Fri, 30 Oct 2015 17:32:23 GMT
    server: Cowboy

    {
        "color": "yellow",
        "name": "bob"
    }

DELETE it:

.. code-block:: sh

    $ http delete localhost:8080/store/mybucket/bob

.. code-block:: http

    HTTP/1.1 204 No Content
    content-length: 0
    content-type: application/json
    date: Fri, 30 Oct 2015 17:32:27 GMT
    server: Cowboy

GET it back to make sure it's actually deleted:

.. code-block:: sh

    $ http localhost:8080/store/mybucket/bob

.. code-block:: http

    HTTP/1.1 404 Not Found
    content-length: 0
    content-type: application/json
    date: Fri, 30 Oct 2015 17:32:28 GMT
    server: Cowboy

DELETE it again to see how it handles a missing delete:

.. code-block:: sh

    $ http delete localhost:8080/store/mybucket/bob

.. code-block:: http

    HTTP/1.1 404 Not Found
    content-length: 0
    content-type: application/json
    date: Fri, 30 Oct 2015 17:43:03 GMT
    server: Cowboy