NoSQLite - SQLite, support for JSON field

Released just recently (14-10-2015) the new SQLite (3.9.x) now has optional support for NoSQL like work flows with the new JSON field type. This means that for certain use cases you don't have to choose SQL or NoSQ database for storing unstructured data. This is similar now to Postgresql, which also has support for BSON and JSON fields.

Let's see how this works. First, you need to download the latest sources of SQLite and compile them with JSON support.

 $ wget
 $ tar xvzf sqlite-autoconf-3090100.tar.gz
 $ cd sqlite-autoconf-3090100.tar.gz
 $ ./configure --enable-json1 --enable-readline 
 $ make
 $ sudo make install

Now, the new SQLite binary will be installed to /usr/local/bin. Let's see how it works:

$ /usr/local/bin/sqlite3 SQLite version 3.9.1 2015-10-16 17:31:12 Enter ".help" for usage hints. Connected to a transient in-memory database. Use ".open FILENAME" to reopen on a persistent database. sqlite> CREATE TABLE testtable (id INTEGER,testfield JSON );

This will create a table with 2 columns, named id and test_field. Having the types of INTEGER and JSON.

Now, let's put some data in the table:

sqlite> insert into test_table (id, test_field) values \
        (1, ' { "this" : "is", "a": [ "test" ] } ');
sqlite> select * from test_table;
1| { "this" : "is", "a": [ "test" ] } 

This works. But there is one caveat, there is not constraint for what's in the json. I could also put junk there. Here is how:

sqlite> insert into test_table (id, test_field) values \
        (2, 'junk text');
sqlite> select * from test_table;
1| { "this" : "is", "a": [ "test" ] } 
2|junk text

OK, you are not impressed. Neither am I. JSON field is basically a text based field. To really use a json field we need to wrap our json with a function call that validates the json. If you are using SQLite within Python, for example, that's a very easy thing to do. In addition, SQLite offers it's own function:

sqlite> insert into test_table (id, test_field) values (1, json('junk text'));
Error: malformed JSON
sqlite> insert into test_table (id, test_field) values (1, json('{"not": "junk"}'));
sqlite> select * from test_table;
1| { "this" : "is", "a": [ "test" ] } 
2|junk text

Does this work the other way too ? Can you put JSON in a text field? Yes you can. But that is expected. The real fun begins when you start extarcting data from json fields. For that, the extension, still widely unknown for the public, provides some functions like:

json_extract(json,path,...) Extract values or subcomponents from a JSON string.
json_insert(json,path,value,...) Insert values into a JSON string without overwriting existing values.
json_object(label1,value1,...) Construct and return a new JSON object based on the arguments.
json_remove(json,path,...) Remove the specified values from a JSON string.
json_replace(json,path,value,...)  Update existing values within a JSON string.
json_set(json,path,value,...)  Insert or replace values in a JSON string. 
                               Overwrite existing elements or create new entries 
                               in the JSON string for elements that do not previously exist.

I am still in the process of learning all those and I'm trying to figure out examples for all those.

Further reading about SQLite's JSON extension.

This entry was tagged: nosql

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