Improve the command execution support

Allow passing an optional database argument besides specifying if POST is required

Author: Enric Sala

README.md

@@ -173,20 +173,20 @@ Notice that the `time()` and `timetable()` methods take an optional timezone arg
 Other commands
 --------------
 
-Use `runCommand(command, requiresPost)` for executing commands not provided in the library:
+Use `runCommand(command, [database], [requiresPost])` for executing arbitrary commands:
 
 ```matlab
-% Show series and tag keys in a database
-influxdb.runCommand('SHOW SERIES ON "example" FROM "weather"');
-influxdb.runCommand('SHOW TAG KEYS ON "example" FROM "weather"');
+% Show databases then create one
+influxdb.runCommand('SHOW DATABASES')
+influxdb.runCommand('CREATE DATABASE "example"', true)
 
-% Create and drop a database
-influxdb.runCommand('CREATE DATABASE "example"', true);
-influxdb.runCommand('DROP DATABASE "example"', true);
+% Show measurements and tag keys
+influxdb.runCommand('SHOW MEASUREMENTS', 'example')
+influxdb.runCommand('SHOW TAG KEYS', 'example')
 
 % Create a retention policy that keeps data for one day
-influxdb.runCommand('CREATE RETENTION POLICY "one_day" ON "example" DURATION 1d REPLICATION 1', true);
-influxdb.runCommand('SHOW RETENTION POLICIES ON "example"', false);
+influxdb.runCommand('CREATE RETENTION POLICY "one_day" ON "example" DURATION 1d REPLICATION 1', true)
+influxdb.runCommand('SHOW RETENTION POLICIES', 'example')
 ```
 
 See the [InfluxDB documentation][influxdb-docs] for more schema exploration and management commands.

influxdb-client/InfluxDB.m

@@ -43,10 +43,7 @@
 
         % Show databases
         function databases = databases(obj)
-            url = [obj.Url '/query'];
-            opts = weboptions('Timeout', obj.ReadTimeout, ...
-                'Username', obj.User, 'Password', obj.Password);
-            response = webread(url, 'q', 'SHOW DATABASES', opts);
+            response = obj.runCommand('SHOW DATABASES');
             databases = [response.results.series.values{:}];
         end
 
@@ -108,15 +105,24 @@
         end
 
         % Execute other queries or commands
-        function response = runCommand(obj, command, requiresPost)
+        function response = runCommand(obj, command, varargin)
+            idx = find(cellfun(@(x) ischar(x), varargin), 1, 'first');
+            database = iif(isempty(idx), '', varargin{idx});
+            idx = find(cellfun(@(x) islogical(x), varargin), 1, 'first');
+            requiresPost = iif(isempty(idx), false, varargin{idx});
+            if isempty(database)
+                params = {'q', command};
+            else
+                params = {'db', database, 'q', command};
+            end
             url = [obj.Url '/query'];
             opts = weboptions('Username', obj.User, 'Password', obj.Password);
-            if nargin > 2 && requiresPost
+            if requiresPost
                 opts.Timeout = obj.WriteTimeout;
-                response = webwrite(url, 'q', command, opts);
+                response = webwrite(url, params{:}, opts);
             else
                 opts.Timeout = obj.ReadTimeout;
-                response = webread(url, 'q', command, opts);
+                response = webread(url, params{:}, opts);
             end
         end
     end