In a previous blog post I showed you how to take a JSON data file and to load it into your Oracle Schema using R. To do this I used ROracle to connect to the database and jsonlite to do the JSON processing of the data.
Alternatives to using ROracle would be RODBC, RJDBC and DBI. So you could use one of these to connect to the database.
In this post I want to show you how to extract data from an Oracle table (or view) and to output it to a file in JSON format. Again I will be using the jsonlite R package to perform all the JSON formatting work for me.
1. Connect to the Database
This is the same connect setup that I used in the previous post.
# initialise the packages
# Create the connection string
“(ADDRESS=(PROTOCOL=tcp)(HOST=”, host, “)(PORT=”, port, “))”,
“(CONNECT_DATA=(SERVICE_NAME=”, service, “)))”, sep = “”)
# establish the connection
2. Read the data from the table/view
Read the data from the table into a R data frame.
 1500 18
> head(data, 3)
CUST_ID CUST_GENDER AGE CUST_MARITAL_STATUS COUNTRY_NAME
1 101501 F 41 NeverM United States of America
2 101502 M 27 NeverM United States of America
3 101503 F 20 NeverM United States of America
CUST_INCOME_LEVEL EDUCATION OCCUPATION HOUSEHOLD_SIZE YRS_RESIDENCE AFFINITY_CARD
1 J: 190,000 – 249,999 Masters Prof. 2 4 0
2 I: 170,000 – 189,999 Bach. Sales 2 3 0
3 H: 150,000 – 169,999 HS-grad Cleric. 2 2 0
BULK_PACK_DISKETTES FLAT_PANEL_MONITOR HOME_THEATER_PACKAGE BOOKKEEPING_APPLICATION
1 1 1 1 1
2 1 1 0 1
3 1 0 0 1
PRINTER_SUPPLIES Y_BOX_GAMES OS_DOC_SET_KANJI
1 1 0 0
2 1 1 0
3 1 1 0
We now have the data from the table in a data frame called data. We can now use this data frame to covert the data into JSON.
3. Convert into JSON format
To produced the JSON formatted output of the data in our table (or view) we can use the toJSON function that produces the outputted JSON data in an R String.
4. Create the JSON file
We are now ready to output the formatted JSON data out to file. We can use the R function ‘write’ to write the JSON data out to a file.
> write(jsonData, file=”c:/app/demo_json_data2.json”)
5. Verify the JSON data was created correctly
To verify that JSON data file was created correctly, we can use the steps outlined in my previous post to read in the file. If all the correct then we should get no errors.
You will notice that there is one difference between the code shown above and what I showed in my previous example/blog post. This time we don’t have an extra wrapper class of Items.
Generating JSON data – Using SQL Developer
In my previous post I showed you one way of generating a JSON file based on the data in a table. You could do that using SQL Developer and SQLcl.
An alternative is to use the Table Export feature to export the data in JSON format.
To do this right click on the table (or view) and select Export from the drop down menu.
The Export Wizard will open. De-select the Export DDL tick box. In the export data section change the format drop-down to JSON. Then enter the location and file name for the JSON file. Then click the next buttons until you are finished.