Instant REST API For Any Database

Jun 16, 2014 / By Yanick Champoux

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Not so long ago, I was playing with ElasticSearch, which has the interesting characteristic of having a REST API as its primary interface. Sure, it’s a little more stilted and awkward than any native interface but, on the other hand, it’s a nice universal type of API. Any language that can make a http request can talk to it and, hey, bad comes to worse, even ‘curl’ will do. It would be kinda cool if other databases had such a web service.

And then I began to think…

Don’t we have DBIx::Class::Schema::Loader, which can connect to a database and auto-generate its DBIx::Class schema?


package MyDB;

use parent 'DBIx::Class::Schema::Loader'; 

...;

# later on

my $schema = MyDB->connect( 'dbi:SQLite:foo.db' ); # boom, we have our schema

And once we have a DBIx::Class representation of a schema, can’t we introspect it and pretty much get everything there is to know about it?


use Data::Printer;

# get all the table names
my @tables = $schema->sources;

# and all the columns of all the tables
for my $table ( $schema->sources ) {
    say "Table $table";
    p $schema->source($table)->columns_info;
}

That is, that’s if we want to do it manually, considering that there’s already SQL::Translator that can do most of the job for us.


use SQL::Translator;

print SQL::Translator->new (
    parser      => 'SQL::Translator::Parser::DBIx::Class',
    parser_args => {
        dbic_schema => $schema,
    },
    producer    => 'JSON',
)->translate;

Of course, since we are talking web service, we will want to pass everything back and forth using JSON, including database entries. Well, that’s hardly a problem if we use DBIx::Class::Helper::Row::ToJSON.

So it seems we have the database side covered. For the web framework? You’ll probably not be surprised to see me go with Dancer. Not only can we leverage the serializers and plugins like Dancer::Plugin::DBIC, but setting routes are ridiculously easy.


get '/_tables' => sub {
    return [ schema->sources ];
};

Even niftier: remember that Dancer routes are defined at runtime, so we can introspect that schema as much as we want and come up with any route we can dream of.


my @primary_key = schema->source($table)->primary_columns;
my $row_url = join '/', undef, $table, ( '*' ) x @primary_key;
 # GET ///
get $row_url => sub {
    my @ids = splat;
    return $schema->resultset($table)->find({
        zip @primary_key, @ids
    });
};
 # GET /
get "/$table" => sub {
    my @things = $schema->resultset($table)->search({ params() })->all;
    return \@things;
};
 # create new entry
post "/$table" => sub {
    $schema->resultset($table)->create({ params() });
};

Added bonus: the way Dancer’s params() conglomerate parameters defined in the query string and in the serialized body of the request plays in our favor: simple queries can be passed directly via the url, and more complicated ones can be defined as JSON structures.

So, you put all of this together, and you obtain waack. All it needs is a dsn pointing to the right database (and credentials, if needed). To illustrate, let’s try with my Digikam SQLite database.


$ waack dbi:SQLite:digikam4.db
>> Dancer 1.3124 server 28914 listening on http://0.0.0.0:3000
>> Dancer::Plugin::DBIC (0.2100)
== Entering the development dance floor ...

And now, let’s fire up App::Presto as our REST client.


$ presto http://enkidu:3000

http://enkidu:3000> type application/json

First, we can retrieve all the table names.


http://enkidu:3000> GET /_tables
[
   "TagsTree",
   "ImageMetadata",
   "Tag",
   "Setting",
   "ImageRelation",
   "ImageTag",
   "ImageProperty",
   "ImageInformation",
   "ImageHaarMatrix",
   "ImageCopyright",
   "VideoMetadata",
   "ImageHistory",
   "DownloadHistory",
   "Search",
   "ImageTagProperty",
   "Image",
   "Album",
   "ImagePosition",
   "TagProperty",
   "AlbumRoot",
   "ImageComment"
]

We can also get the whole schema.


http://enkidu:3000> GET /_schema
{
   "translator" : {
      "producer_args" : {},
      "show_warnings" : 0,
      "add_drop_table" : 0,
      "parser_args" : {
         "dbic_schema" : null
      },
      "filename" : null,
      "no_comments" : 0,
      "version" : "0.11018",
      "parser_type" : "SQL::Translator::Parser::DBIx::Class",
      "trace" : 0,
      "producer_type" : "SQL::Translator::Producer::JSON"
   },
   "schema" : {
      "tables" : {
         "ImageRelations" : {
            "options" : [],
            "indices" : [],
            "order" : "12",
            "name" : "ImageRelations",
            "constraints" : [
               {
                  "type" : "UNIQUE",
                  "deferrable" : 1,
                  "name" : "subject_object_type_unique",
                  "on_delete" : "",
                  "reference_fields" : [],
                  "fields" : [
                     "subject",
                     "object",
                     "type"
                  ],
                  "match_type" : "",
                  "reference_table" : "",
                  "options" : [],
                  "expression" : "",
                  "on_update" : ""
               }
            ],
...

Too much? We can get the columns of a single table.


http://enkidu:3000> GET /Tag/_schema
{
   "iconkde" : {
      "is_nullable" : 1,
      "data_type" : "text",
      "is_serializable" : 1
   },
   "name" : {
      "is_serializable" : 1,
      "data_type" : "text",
      "is_nullable" : 0
   },
   "id" : {
      "is_nullable" : 0,
      "data_type" : "integer",
      "is_auto_increment" : 1,
      "is_serializable" : 1
   },
   "icon" : {
      "is_nullable" : 1,
      "data_type" : "integer",
      "is_serializable" : 1
   },
   "pid" : {
      "is_serializable" : 1,
      "is_nullable" : 1,
      "data_type" : "integer"
   }
}

Query that table, with a simple condition…


http://enkidu:3000> GET /Tag id=1
[
   {
      "name" : "orchid",
      "icon" : null,
      "id" : 1,
      "pid" : 0,
      "iconkde" : null
   }
]

… or with something a little more oomphie.


$ curl -XGET -H Content-Type:application/json --data '{"name":{"LIKE":"%bulbo%"}}' http://enkidu:3000/Tag
[
   {
      "pid" : 1,
      "name" : "Bulbophyllum 'Melting Point'",
      "icon" : null,
      "id" : 32,
      "iconkde" : "/home/yanick/Pictures/My Plants/IMG_0461.JPG"
   },
   {
      "id" : 56,
      "iconkde" : "tag",
      "icon" : null,
      "pid" : 39,
      "name" : "Bulbophyllum ebergardetii"
   },
   {
      "name" : "bulbophyllum",
      "pid" : 564,
      "iconkde" : null,
      "id" : 565,
      "icon" : 0
   }
]

Btw: I cheated for that last one. Presto doesn’t send body with GET requests. And Dancer doesn’t deserialize GET bodies either. Patches will be written tonight.

Anyway, back with the show. We can also select specific rows by primary keys.


http://enkidu:3000> GET /Tag/1
{
   "id" : 1,
   "iconkde" : null,
   "pid" : 0,
   "icon" : null,
   "name" : "orchid"
}

Create new rows.


http://enkidu:3000> POST /Tag '{"name":"nepenthes","pid":0}'
{
   "pid" : 0,
   "name" : "nepenthes",
   "iconkde" : null,
   "icon" : null,
   "id" : 569
}

And do updates.


http://enkidu:3000> PUT /Tag/569 '{"icon":"img.png"}'
{
   "icon" : "img.png",
   "iconkde" : null,
   "pid" : 0,
   "name" : "nepenthes",
   "id" : 569
}

Not too shabby, isn’t? Mostly considering that, if you look at the source of waack, you’ll see that it barely clock over 100 lines of code. Take a minute and let this sink in.

One hundred lines of code. For a universal database REST web service.

If that’s not standing on the shoulders of giants, then I don’t know what is.

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