Looking for method that projects variables into SQLibrary execute command.

Programming Questions

kaihansen..

Looking for method that projects variables into SQLibrary execute command.

in Programming Questions • 1 year ago

Hello,

Is there a way to project updated values into a SQL command string? I'm accessing web-based XML data every ten minutes and want to write it to my PostgreSQL DB.

This would be the example command to write to DB:

pgsql.execute(INSERT INTO table (column1, column2, etc) VALUES (value1, value2, ect));

For these variables:

String station_location_xml;

String observation_time_xml;

String temp_f_xml;

String temp_c_xml;

String relative_humidity_xml;

String wind_degrees_xml;

String wind_dir_xml;

String wind_mph_xml;

String wind_gust_mph_xml;

String dewpoint_f_xml;

String dewpoint_c_xml;

I want to write into the DB, which could look like:

pgsql.execute( "INSERT INTO adaptive_weather_longterm (station_location, observation_time, temp_f, temp_c, relative_humidity, wind_dir, wind_mph, wind_gust_mph, dewpoint_f, dewpoint_c) VALUES ('" + station_location_xml + "', '" + observation_time_xml + "', '" + temp_f_xml + "', '" + temp_c_xml + "', '" + relative_humidity_xml + "', '" + wind_dir_xml + "', '" + wind_mph_xml + "', '" + wind_gust_mph_xml + "', '" + dewpoint_f_xml + "', '" + dewpoint_c_xml + "')");

Except, the library requires a straight up string here for "VALUES".

I've tried coding:

String sqlCommand = new String ("INSERT INTO adaptive_weather_longterm (station_location, observation_time, temp_f, temp_c, relative_humidity, wind_dir, wind_mph, wind_gust_mph, dewpoint_f, dewpoint_c) VALUES ('" + station_location_xml + "', '" + observation_time_xml + "', '" + temp_f_xml + "', '" + temp_c_xml + "', '" + relative_humidity_xml + "', '" + wind_dir_xml + "', '" + wind_mph_xml + "', '" + wind_gust_mph_xml + "', '" + dewpoint_f_xml + "', '" + dewpoint_c_xml + "')");

return (sqlCommand);

Then calling the variable:

pgsql.execute(sqlCommand);

However, I'm met with " Exception in thread "Animation Thread" java.lang.NullPointerException".

This is a problem since this data is not static. How can I get the dynamic values into this string???

Is there a new method I can add to the source?

Thanks in advance!

Replies(5)

PhiLho

Re: Looking for method that projects variables into SQLibrary execute command.

1 year ago

new String("a string") is useless, it is just like "a string". Otherwise, the sqlCommand construction seems to be OK.

You say you have a null pointer exception, but we don't know on what code.
See if the article Why do I get a NullPointerException? can help you there.

I don't understand your static vs. dynamic question...

kaihansen..

Re: Looking for method that projects variables into SQLibrary execute command.

1 year ago

The null pointer exception is directly related to "pgsql.execute(sqlCommand);", or so I figure. The program runs w/o issue until I introduce this function. I think you pointed out in my other thread that the SQLibrary can only take a string. I was hoping that I could substitute the explicit string with a stored string value (in this case sqlCommand), but that doesn't seem to work and produces the null pointer exception.

The point I was trying to make with static v. dynamic is that the SQLibrary appears to be set up for a one-time input or write to the DB (static). In my case, I want to constantly update it (dynamic). What I'm trying to figure out is how I can record this "dynamic" data using pgsql.execute() when the required input for it apparently needs to be a pre-defined string? I assume that using this variable in place of the expected string is what's causing the null pointer exception.

If you look under the " I want to write into the DB, which could look like " heading you should see that I'm trying to insert the variables temp_f_xml, temp_c_xml, etc. into the string. It doesn't work either, but should illustrate my goal.

PhiLho

Re: Looking for method that projects variables into SQLibrary execute command.

1 year ago

Sometime, the error can be simple, like having two (or more!) different declarations of sqlCommand, and not using the returned one... Hard to tell without the full code. And without the full exception trace.

And sending to a thread by its name is a bit awkward... That's the inconvenience of starting several threads...

kaihansen..

Re: Looking for method that projects variables into SQLibrary execute command.

1 year ago

I'm sorry....

It shan't happen again.

It made sense at the time though, since I was looking for a more specific answer than what the previous thread title suggested.

You were right again though. I had declared the variable in the main tab above void setup(), and again in the function that creates the string sqlCommand. Thanks for all your help.

PhiLho

Re: Looking for method that projects variables into SQLibrary execute command.

1 year ago

Glad you solved your problem. And FYI, I think you can edit your first message to change its title, if needed.

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