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Category: JSON

Transforming JSON to CSV with Azure Data Factory

Rayis Imayev shows how you can use the Flatten task in Azure Data Factory to convert JSON text to CSV:

What this new task does it helps to transform/transpose/flatten your JSON structure into a denormalized flatten datasets that you can upload into a new or existing flat database table. 

I like the analogy of the Transpose function in Excel that helps to rotate your vertical set of data pairs (name : value) into a table with the column names and values for corresponding objects. And when this vertical JSON structural set contains several similar sets (array) then ADF Mapping Data Flows Flatten does a really good job by transforming it into a table with several rows (records).

Click through for a demonstration.

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Parsing ADF ARM Templates with T-SQL

Paul Andrew shows how you can use T-SQL to read an Azure Data Factory ARM template:

While documenting a customers data platform solution I decided it would be far easier if we could summarise the contents of a fairly complex Data Factory using its ARM Template. So, this is what I’ve done using T-SQL to parse the ARM Template JSON and output of series of tables containing details about the factory components.

That is quite the clever solution.

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Automating JSON to Tables

Dave Mason has a stored procedure for us:

The code for my stored procedure is below. It has a single input parameter for a string of JSON data. The name/value pairs of the first “row” of JSON data is parsed to obtain column names and types for the result set. A query string for the OPENJSON function is constructed and executed via EXEC. JSON’s support for data types is pretty sparse compared to SQL Server (notice the big CASE expression where I attempt to do some mapping). If you’re using SQL 2016, you’ll have to make an edit for the STRING_AGG function.

Click through for the code and demos.

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When FOR JSON PATH Isn’t Enough

Dave Mason walks us through some options when working with JSON data in SQL Server:

In both situations, we need to know something about the JSON schema to query it in a meaningful way: in the first example, column names and types are hard-coded; in the second example, column names are hard-coded as path parameter values for the JSON_VALUE function. Even though JSON data is self-describing, SQL Server doesn’t have a way to infer schema. (I would be quite happy to be wrong about this–please add a comment if you know something I don’t!) About the time I came to this realization, I commented on Twitter that JSON might be fool’s gold. You don’t need to know schema to store JSON data in SQL Server. But you do if you want to query it. “It’s pay me now or pay me later.”

It’s schema on read or schema on write. I’m not sure there is ever a truly schema-free scenario in a business application.

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Using SQL Server as a REST API Back-End

Davide Mauri shows how you can use SQL Server to power an API, using Flask as an example:

I mentioned in my previous article that having native JSON support in Azure SQL it’s a game changer as it profoundly change the way a developer can interact with a relational database, bringing the simplicity and the flexibility needed in today’s Modern Applications.

As Python is becoming immensely popular, one of the most common tasks for a developer is to create REST API using Python. Thanks to JSON support, using Azure SQL as a backend database to support your API is as easy as writing to a text file, with the difference that behind the scenes you have all the peace of mind that your data will be safely stored and made available on request, at scale, with also the option to push as much compute to data as you want, so that you can leverage the powerful query and processing engine while keeping your code simple, elegant and agile, with a clear separation of concerns. All these things will help you immensely once you’ll start to evolve your project to keep it updated with today’s demanding and ever-changing world.

Those who remember the days of ASMX web services in SQL Server (thankfully removed after 2005) might cringe, but I’ve actually done something like this for a company, where all of the data lived in SQL Server and the transformation logic was pretty simple. If you have to monkey with the JSON afterward in your middle tier, then just bring back a data set, but in a scenario like Davide shows, moving the JSON creation to Python wouldn’t really gain you anything.

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Managing SQL Server Documentation with JSON

Phil Factor gives us the gloop:

Metadata extract files are handy for documentation, study, cataloguing and change-tracking. This type of file supplements source because it can record configuration, permissions, dependencies and documentation much more clearly. It is a good way of making a start with documenting your database.

Here is a sample of a json metadata file (from AdventureWorks 2016). It was generated using GloopCollectionOfObjects.sql that is here in Github, and is being viewed in JSONBuddy. I use this format of JSON, a collection of documents representing SQL Server base objects (no parent objects) when I need to read the contents into MongoDB. The term ‘Gloop’ refers to a large query that, you’d have thought, would be better off as a procedure. Here is a typical sample of the output.

This is an interesting approach to documentation. I’m not totally buying into it, but that might just be due to my not having tried it.

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Use SQL for XML and JSON Creation

Lukas Eder argues that if you’re storing the data in SQL and you need to get data from a database into JSON or XML format, just use SQL for that:

In English: We need a list of actors, and the film categories they played in, and grouped in each category, the individual films they played in.

Let me show you how easy this is with SQL Server SQL (all other database dialects can do it these days, I just happen to have a SQL Server example ready:

Lukas makes a great point and has a FAQ to follow up on it. If there’s a reason for mapping at a higher layer—if you’re actually adding value rather than building out a set of converters—that’s one thing, but if you’re just accepting a data set and returning a JSON blob…well, your database product can do that too.

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Storing Database Deployment Metadata with JSON

Phil Factor combines a couple SQL Server features to track database deployment history:

We maintain the current record where it is easy to get to and simply add an array to hold the history information. Our only headache is that we can only hold an NVARCHAR of 3750 characters (7500 of varchar characters) because extended properties are held as SQL_Variants. They need careful handling! This means that if our JSON data is larger, we have to trim off array elements that make the JSON exceed that number.

The combination of JSON and extended properties is not one that I’ve seen before—typically, there’s a deployment log table.

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Benchmarking JSON Query Times

Silvano Coriani compares different options for loading and querying JSON data in Azure SQL Database:

Storing and retrieving data from JSON fragments is a common need in many application scenarios, like IoT solutions or microservice-based architectures. These fragments can be persisted in a variety of data stores, from blob or file shares, to relational and non-relational databases, and there’s a long standing debate in the industry on what’s the database technology that fits “better” for this task.
Azure SQL Database offers several options for parsing, transforming and querying JSON data, and this article doesn’t pretend to provide a definitive answer to that debate, but rather to explore these options for common scenarios like data loading and retrieving, and benchmarking results to provide a clear indication of how Azure SQL Database will perform manipulating JSON data.

Read on for the results.

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Converting JSON to Result Sets

Jack Vamvas shows how you can import data in JSON format and get tabular data in SQL Server:

It is possible to read a json file using T-SQL.There are a number of different methods.  By using the OPENROWSET functionality , ISJSON and OPENJSON function you can quickly read the file , check if the JSON is valid and then unpack the JSON into a SQL table. 

Read on for an example. This also performs reasonably well in practice, at least in my experience.

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