Thursday, August 29, 2019

The Two Aspects of Db2 for z/OS Support for JSON Data

JSON (JavaScript Object Notation) is a form of data representation that is popular with people who develop what you might call "very modern" applications, including those that are cloud-based and those that have a mobile front-end. One reason this is so: a JSON document is easy for a program (or a person) to parse, as you'll see from examples I've included a bit further down in this blog entry.

As interest in JSON has grown, more folks have asked about the support that Db2 for z/OS provides for data represented in this form. I'm going to tell you about that support, starting with the fact that it comes in two flavors (which can be used separately or together). First, there is the JSON support that is associated with Db2's REST interface. The other flavor of Db2 REST support has to do with storing JSON documents, as such, in a column of a Db2 table. I'll cover these two REST-related Db2 capabilities in the order of my having mentioned them.

JSON and the REST interface to Db2 for z/OS

Through Db2's REST interface, you can enable execution of a static SQL statement via a REST request (for those not familiar with Db2 "static" SQL: the term refers to a statement that has been pre-coded and pre-prepared for execution - it's basically the compiled, executable form of a SQL statement). That SQL statement could be a SELECT, INSERT, UPDATE, DELETE or TRUNCATE, or a CALL to a stored procedure (the called stored procedure could then issue any number of different SQL statements). Let's consider a situation in which a SELECT that retrieves information about a bank account has been REST-enabled (sensitive information, yes, but Db2's REST interface utilizes connection protection and authentication services provided by the RACF z/OS security manager, along with Db2's own user authorization functionality). If this SELECT-based service is named getAcctInfo, the associated REST request issued by a client program could look like this:


And in the body of the request you might see this input:

 “AcctID”: 123456789

That input is in the form of a JSON document - a very small JSON document, comprised of just a single name-value pair. Without being a rocket scientist, you can look at that JSON document and figure out that 123456789 is someone's account ID. That ease-of-interpretation is one of the appealing characteristics of JSON versus, say, XML. XML tags are sometimes kind of obtuse, owing in part to the fact that there often has to be broad agreement as to the meaning of a given tag (something that makes XML a very robust form of representation for data that might be exchanged between different companies, such as an automobile manufacturer and a parts supplier). With regard to the data payload of a REST request in JSON form, there just has to be agreement on meaning between client and server, and that flexibility enables use of meaningful names in name-value pairs.

OK, so that REST request, with its input in JSON form, comes into a Db2 for z/OS system (the system associated with in the HTTP request). Assuming that the request's credentials check out (that would be ID and password, or ID and certificate), and the ID has been granted EXECUTE authority for the Db2 package that is the executable form of the REST-enabled SQL statement, the provided input will get plugged into the SELECT and the statement will be executed. Let's say the SELECT - with the provided input added - looks like this:

WHERE A.ID=123456789


Suppose that the query's output looks like this, in traditional SQL result set form:

---------    --------    -------    -------
John         Smith       1982.42    3000.00

Db2 will take that result set and send it back to the REST client in the form of a JSON document, as seen below (if the REST-enabled query had a multi-row result set, you'd see multiple sets of associated name-value pairs, one after another in the JSON output document):

  “FIRSTNAME” : “John”,
  “LASTNAME”  : “Smith”,
  “BALANCE”   : 1982.42,
  “LIMIT”     : 3000.00

That, then, is the one aspect of Db2 for z/OS support for data in JSON form: as a provider of data services invoked via REST requests, Db2 accepts input in JSON form and sends output to a requester in JSON form. Now for a look at the other aspect of Db2 for z/OS support for JSON data.

Storing JSON documents in Db2 tables

Suppose that a client application sends data in JSON form to a z/OS server, and there is a desire to store those JSON documents as values in a column of a Db2 table. Db2 provides support for that usage scenario by way of some user-defined functions (UDFs) supplied via a no-charge software offering called the IBM Db2 Accessories Suite for z/OS (Version 4.1 of which is the one that goes with Db2 12 for z/OS - the product number is 5697-Q05). The most important of these UDFs are JSON2BSON, BSON2JSON and JSON_VAL. Here is what they do:

  • JSON2BSON - Converts a JSON document to BSON (a standard binary form for JSON data), so that it can be stored in a Db2 table column defined with the BLOB data type.
  • BSON2JSON - This UDF can be used to retrieve a JSON document in its entirety from a Db2 BLOB column in which the document is stored in BSON form. Output of the function is the text form of the retrieved JSON document.
  • JSON_VAL - This function can be used to retrieve - or to refer to - an individual data item (e.g., LASTNAME) in a JSON document. In addition to being usable in a query's select-list, JSON_VAL can be referenced in a predicate of a SELECT, INSERT or DELETE (you could, for example, retrieve data from a table based on the value of a particular item in a JSON document). JSON_VAL can also be used in a case expression or an ORDER BY clause; and, the function can be utilized to create an index on a table column that holds JSON documents (similar in concept to an index on an XML column - you might want an index on customer number values in JSON documents in a column).

Other UDFs that pertain to JSON data stored in a Db2 table are JSON_LEN, JSON_TYPE and JSON_TABLE. You can get additional information about all of the JSON-related UDFs in the Db2 for z/OS Knowledge Center on the Web.

And there you have it. As a data services provider for applications that use the REST architectural style, Db2 for z/OS can build a JSON document from data in a Db2 database, with said JSON document then used to return data to a REST client (and a REST client invoking a Db2-provided service can send associated input data in a JSON document). Db2 for z/OS also provides (in conjunction with the IBM Db2 Accessories Suite for z/OS) the ability to store JSON documents in Db2 tables, and to work with those documents (and the data values therein) using SQL. Two different areas of JSON-related functionality, each of which can be valuable for addressing different requirements that involve data in JSON form. I encourage you to explore and evaluate these capabilities.

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