Database HowTo - How to load a JSON document in a database
A propos
This howto will show you how to load json document (files) into a relational database.
This example uses the sqlite howto database but you may use any other relational database
Steps
The Json files
To be able to follow along the SQLite examples of the JSON documentation, we will load phones numbers in a user table.
The JSON files are located in the subdirectory json/phone of the howto directory where there is one file by user containing a JSON array of phones.
With the data list command, we can list them.
tabli data list json/phone/*.json@howto
path
----------------------
json\phone\Arnold.json
json\phone\Bob.json
json\phone\Dale.json
json\phone\Daniel.json
json\phone\Don.json
With the data print command, we can see for instance the JSON array of phones in the Bob.json file
tabli data print json/phone/Bob.json@howto
["323-423-2238","747-444-3222","475-202-7142"]
Json relational structure
By default, a json file is seen as a relation with one column called json
The structure of the JSON file can be seen with the data struct command.
For instance, for the Don.json file, there is one column:
- at the position 1
- called json
- with the json data type
tabli data struct json/phone/Don.json@howto
Structure of the resource json\phone\Don.json@howto
position name data_type precision scale primary_key nullable autoincrement comment
-------- ---- --------- --------- ----- ----------- -------- ------------- -------
1 json json x false
Loading the JSON files
The below data insert command will load the JSON files into the phones table of the sqlite howto database.
tabli data insert json/phone/*.json@howto user@sqlite
Source Target Latency (ms) Row Count Error Message
---------------------------- ----------- ------------ --------- ----- -------
json\phone\Arnold.json@howto user@sqlite 10 1
json\phone\Bob.json@howto user@sqlite 12 1
json\phone\Dale.json@howto user@sqlite 11 1
json\phone\Daniel.json@howto user@sqlite 11 1
json\phone\Don.json@howto user@sqlite 29 1
You can inspect the content with the head command
tabli data head user@sqlite
The first 10 rows of the data resource (user@sqlite):
json
-----------------------------------------------
["470-293-7517"]
["323-423-2238","747-444-3222","475-202-7142"]
["704-555-0150","202-555-0150"]
["425-898-3481","360-637-7972", "205-533-8271"]
["731-414-7236","256-233-3557","409-645-3618"]
Changing the name of the JSON column
The name of the JSON column is by default json but we can change it by setting the columnName json attribute
After running the below head command, we can see that the column name has changed to phones
tabli data head --attribute columnName=phone json/phone/Don.json@howto
The first 10 rows of the data resource (json\phone\Don.json@howto):
phone
----------------
["470-293-7517"]
Adding a column with the logical name of the JSON file
Because the JSON content of files does not have any kind of identifier, we can see that the data is actually worthless because we can't relate the phone to a user.
To be able to add context to file loaded, Tabulify supports the concept of virtual columns where it's possible to add any attribute information about the file loaded.
The virtual columns are specified with the –virtual-column option that has the following syntax:
--virtual-column virtualColumnName=resourceAttributeName
where:
- virtualColumnName is the name of the column added
- resourceAttributeName is the name of resource attribute.
For instance, if we want to add:
- into a column called name,
we would add –virtual-column name=logical_name
With the print command, the full command would look like below.
tabli data print --attribute columnName=phone --virtual-column name=logical_name json/phone/Bob.json@howto
phone name
---------------------------------------------- ----
["323-423-2238","747-444-3222","475-202-7142"] Bob
Reloading the JSON files with the virtual column name
To reload the JSON files:
- with the extra column name and the file logical name
- with a column phones containing the JSON document
the syntax of the tabli data insert would be:
tabli data insert --target-operation replace --source-attribute columnName=phone --virtual-column name=logical_name json/phone/*@howto user@sqlite
where:
- --target-operation will replace the target phones@sqlite
- --source-attribute columnName=phones will set the JSON attribute columnName to phones
- --virtual-column name=logical_name will add the virtual column names name with the logical name attribute of the source
- json/phone/*@howto is the source data selector
- phones@sqlite is the target uri
Output:
Source Target Latency (ms) Row Count Error Message
---------------------------- ----------- ------------ --------- ----- -------
json\phone\Arnold.json@howto user@sqlite 15 1
json\phone\Bob.json@howto user@sqlite 14 1
json\phone\Dale.json@howto user@sqlite 16 1
json\phone\Daniel.json@howto user@sqlite 14 1
json\phone\Don.json@howto user@sqlite 37 1
The JSON data loaded has now the name column as identifier.
tabli data print user@sqlite
phone name
----------------------------------------------- ------
["470-293-7517"] Don
["323-423-2238","747-444-3222","475-202-7142"] Bob
["704-555-0150","202-555-0150"] Arnold
["425-898-3481","360-637-7972", "205-533-8271"] Daniel
["731-414-7236","256-233-3557","409-645-3618"] Dale
Performing JSON SQL statement
Inspired from the SQLite examples of the JSON documentation - section 4.3.1, we will now run the below SQL with JSON function.
-- https://www.sqlite.org/json1.html#examples_using_json_each_and_json_tree_
SELECT DISTINCT user.name
FROM user, json_each(user.phone)
WHERE json_each.value LIKE '704-%';
To see the result of this SQL query, we will use the print command and see that Arnold is the user that have a phone number that starts with 704.
tabli data print (sqlite/user_phone_json.sql@howto)@sqlite
name
------
Arnold
Next
- If you want to explore the JSON SQL function of SQLite, you can read the Sqlite JSON documentation.
- A JSON file containing an JSON object can also be loaded with its first properties representing columns. To do that, you need to set the structure attribute to properties.