APEX_JSON.PARSE Issue with CLOBs and 11g

Update: this issue is documented on the APEX 5 Known Issues page (bug 20974582) and has a patch for users with access to MOS (bug 20931298).

APEX 5.0 comes with some new APIs including APEX_JSON which manages JSON files.

When using APEX_JSON to consume a JSON file, the process is fairly straight forward:

  • Parse: This parses the JSON and stores it in a record type.
  • Read values in the JSON object by providing the path to each name/value pair.

The APEX_JSON documentation has some great examples which covers the above process in more details.

There is one "bug" that I found with APEX_JSON.PARSE when passing in a CLOB that has more than 8191 characters. The reason is APEX_JSON.PARSE uses DBMS_LOB.SUBSTR behind the scenes which has a known bug in 11g R1, 11g R2, and 11g XE. In 12c onwards, this is not an issue. An example of the error that is raised is:

ORA-20987: Error at line 626, col19: Expected ":", seeing "<varchar2>"

ORA-06512: at "APEX_050000.WWV_FLOW_JSON", line 292
ORA-06512: at "APEX_050000.WWV_FLOW_JSON", line 560
ORA-06512: at "APEX_050000.WWV_FLOW_JSON", line 756
ORA-06512: at "APEX_050000.WWV_FLOW_JSON", line 774
ORA-06512: at "APEX_050000.WWV_FLOW_JSON", line 624
ORA-06512: at "APEX_050000.WWV_FLOW_JSON", line 719
ORA-06512: at "APEX_050000.WWV_FLOW_JSON", line 615
ORA-06512: at "APEX_050000.WWV_FLOW_JSON", line 758
ORA-06512: at "APEX_050000.WWV_FLOW_JSON", line 774
ORA-06512: at "APEX_050000.WWV_FLOW_JSON", line 811
ORA-06512: at "APEX_050000.WWV_FLOW_JSON", line 887
ORA-06512: at line 24

The APEX_JSON.PARSE procedure currently has two supported overloaded methods. One which takes in a varchar2, and the other which takes in a CLOB. Thankfully there's a third (undocumented) method which takes in a table of varchar2. Note: in future versions of APEX, this may be a supported procedure.

Here's a sample snippet on how to convert your CLOB to a varchar2 table and then call APEX_JSON.PARSE:

  l_clob clob;
  l_json apex_json.t_values;

  l_temp varchar2(1000);

  l_clob_tab apex_application_global.vc_arr2;


  l_clob := 'load json data here';

  -- Convert clobtotable
    c_max_vc2_size pls_integer := 8100; -- Bug with dbms_lob.substr 8191

    l_offset pls_integer := 1;
    l_clob_length pls_integer;
    l_clob_length := dbms_lob.getlength(l_clob);

    while l_offset <= l_clob_length loop
      l_clob_tab(l_clob_tab.count + 1) :=
        dbms_lob.substr (
         lob_loc => l_clob,
         amount => least(c_max_vc2_size, l_clob_length - l_offset +1 ),
         offset => l_offset);

      l_offset := l_offset + c_max_vc2_size;
    end loop;

  -- Parse clob as JSON
    p_values => l_json,
    p_source => l_clob_tab,
    p_strict => true);

  -- You can now use the JSON object for l_json

Note: the code to convert the CLOB to the table will be available soon as part of the new OraOpenSource OOS_UTILS project.

Thanks to Christian Neumüller for helping resolve this issue.