Updating things in Riak using Erlang

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This article is based on Riak 0.71. It assumes you have a running Riak server and a working Erlang client, and that you have completed the tutorial on storing things in Riak.

So you know that Riak stores things in buckets and that these things are key-value pairs. We will go over these basics again. Start by launching Erlang :

erts-5.7.4/bin/erl -name riaktest -setcookie riak

: which should  take you to the Erlang shell. Then enter :

{ok, RiakClient} = riak:client_connect('riak@192.168.1.4').

: which should return something like :

{ok,{riak_client,'riak@192.168.1.4',<<7,148,98,13>>}}

: Then see what is in Riak ( assuming you have already done the storing things in Riak tutorial) :

RiakClient:list_buckets( ).

: which should return :

{ok,[<<"right_hand_bucket">>,

<<"left_hand_bucket">>]}

Lets create a new Bucket called all_sorts_of_things_in_here with a favorite films list in it :

FavoriteFilmsItem =

riak_object:new(<<"all_sorts_of_things_in_here">>, <<"favorite_films">>, ["star wars"]).

RiakClient:put( FavoriteFilmsItem , 1).

: and if successful we get back :

ok

Then, just to show that the new bucket has been created :

RiakClient:list_buckets( ).

: should result in something like :

{ok,[<<"right_hand_bucket">>,
<<"all_sorts_of_things_in_here">>,
<<"left_hand_bucket">>]}

Then check the what is in this new bucket :

RiakClient:list_keys(<<"all_sorts_of_things_in_here">>).

: which should return :

{ok,[<<"favorite_films">>]}

Then to read back the value of favorite films use :

{ ok, FavoriteFilmsItem2 } = RiakClient:get(
    <<"all_sorts_of_things_in_here">>,
    <<"favorite_films">>,
    1).

FavoriteFilmsItem2.

: and you will get the value of FavoriteFilmsItem2 as :

{r_object,<<"all_sorts_of_things_in_here">>,

<<"favorite_films">>,

[{r_content,{dict,2,16,16,8,80,48,

{[],[],[],[],[],[],[],[],[],[],[],[],[],[],...},

{{[],[],[],[],[],[],[],[],[],[],[[...]],[],...}}},

["star wars"]}],

[{<<7,148,98,13>>,{1,63433803807}}],

{dict,1,16,16,8,80,48,

{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],...},

{{[],[],[],[],[],[],[],[],[],[],[],[],[],...}}},

undefined}

: so what does all this mean? Well, maybe its best just to get the value out for now:

FavoriteFilmsValue = riak_object:get_value( FavoriteFilmsItem2 ).

: which should return :

["star wars"]

So, what if we have another film we want to add to out list of favorites? Well, first we need a new list with the new film in it. So we do this in Erlang with :

UpdatedFavoriteFilmsValue = ["Terminator" | FavoriteFilmsValue].

so the new list can be seen by entering:

UpdatedFavoriteFilmsValue.

: returning :

["Terminator","star wars"]

Then we need to do the following:

UpdatedFavoriteFilmsItem = riak_object:update_value(
    FavoriteFilmsItem,
    UpdatedFavoriteFilmsValue).

RiakClient:put( UpdatedFavoriteFilmsItem, 1).

: and the Erlang command prompt should indicate success with :

ok

now if you look at the favorite films:

{ ok, UpdatedFavoriteFilmsItem2 } = RiakClient:get(
    <<"all_sorts_of_things_in_here">>,
    <<"favorite_films">>, 1).

riak_object:get_value( UpdatedFavoriteFilmsItem2 ).

: shows :

["Terminator","star wars"]

Next, if we want to delete the list of films:

RiakClient:delete(<<"all_sorts_of_things_in_here">>, <<"favorite_films">>,1).

: should return :

ok

: and then confirm that :

RiakClient:list_keys( <<"all_sorts_of_things_in_here">> ).                  

: returns :

{ok,[ ]}

Also, try:

RiakClient:list_buckets( ).

: should return :

{ok,[<<"right_hand_bucket">>,
<<"left_hand_bucket">>]}

This shows that the bucket all_sorts_of_things_in_here does not exist anymore either. This is because buckets in Riak are really just a prefix to keys and unlike in real life, buckets in Riak cannot exists without any keys in them.

So in this article you have used the following new commands:

{ ok, UpdatedFavoriteFilmsItem } = RiakClient:get(<<"all_sorts_of_things_in_here">>, <<"favorite_films">>, 1).

UpdatedFavoriteFilmsValue = ["Terminator" | FavoriteFilmsValue].

TheFilmsValue = riak_object:get_value( TheFilms ).

UpdatedFavoriteFilmsObject = riak_object:update_value(FavoriteFilmsObject, TheNewListOfFilms).

RiakClient:delete(<<"all_sorts_of_things_in_here">>, <<"favorite_films">>,1).