Create a Pipeline

How pipelines work

Pipelines are the fundamental building blocks of your Hop projects.

Pipelines perform the heavy lifting: they read data from a variety of sources, perform a number of operations (combine, clean, enrich, transform etc) and write the data out to some target platform. A pipeline executes all of these operations in a predefined order and in parallel.

In the image below, a very simple pipeline reads data from a database, adds a message to the data and sends out an email. All of these operations are executed in a predefined order (read from the database, add the message, send the mail) and in parallel. The pipelines executes these transforms, Imagine our database table or query contains thousands of rows. The pipeline will start reading results from the query, pass those on to the ‘Add message’ transform. Once the message has been added, we’ll send a mail from the Mail transform. All of these will operate in parallel, so the Mail transform will already be sending mails while the table input is still reading records from the table or query.

Concepts

Pipelines consist of transforms connected by hops. In the mail example ‘Table input’, ‘Add message’ and ‘Mail’ are all transforms.

• transforms are the basic operations in your pipeline. A pipeline typically consists of a lot of transforms that are chained together by hops. Transforms are granular, in the sense that each transform is designed and optimized to perform one and only one task. Although one transform by itself may not offer spectacular functionality, the combination of all transforms in a pipeline is makes your pipelines powerful.

• hops link transforms together. When a transform finishes processing the data set it received, that data set is passed to the next transform through a hop. Hops are uni-directional (data can’t flow backwards). Hops only buffer and pass data around, the hop itself is transform-agnostic, it doesn’t know anything about the transforms it passes data from or to. Some transforms can read from or write to other transforms conditionally to or from a number of other transforms, but this a transform-specific configuration. The hop is unaware of it. Hops can be disabled by clicking on them, or through right-click → disable.

Create a pipeline

Create a new pipeline through the work item dialog. You’ll be presented with the dialog shown below.

When you are finished with your pipeline, save it. This can be done via the File menu, the icons or using CTLR s or Command s. For new pipelines a file browser is displayed to navigate towards the location you want to store the file.

Add Transform to your pipelines

Click anywhere in the pipeline canvas, the area where you’ll see the image below.

Upon clicking, you’ll be presented with the dialog shown below. The search box at the top of this dialog works for transform, name, tags (TODO) etc. Once you’ve found the transform you’re looking for, click on it to add it to your pipeline. An alternative to clicking is arrow key navigation + enter. Repeat this step now or whenever you want to add more transforms to your pipeline. Once you’ve added a transform to your pipeline, you can drag to reposition it.

Check the list of transforms to add to your pipeline for more details.

Add a ‘Generate Rows’ and a ‘Add Sequence’ transform, and your pipeline should like the one below.

The transform object can be configured through a single click on the object. The menu displayed below will be shown based on your transform object.

Add a Hop between transforms

There are a number of ways to create a hop:

• shift-drag: while holding down the shift key on your keyboard. Click on a transform, while holding down your primary mouse button, drag to the second transform. Release the primary mouse button and the shift key.

• scroll-drag: scroll-click on a transform , while holding down your mouse’s scroll button, drag to the second transform. Release the scroll button.

• click on a transform in your pipeline to open the ‘click anywhere’ dialog. Click the ‘Create hop’ image::getting-started/icons/HOP.svg[Create hop, 25px, align=”bottom”] button and select the transform you want to create the hop to.

Some transforms result in different types of hops.

Pipeline properties

Pipeline properties are a collection of properties that describe the pipeline and configure its behavior.

The properties dialog can be opened by double clicking on the pipeline canvas.

Following properties can be configured:

• Pipeline

• Parameters

• Monitoring

The Pipeline tab allows you to specify general properties about the pipeline including:

The parameters tab allows you to specify parameters specific for the pipeline. Parameters are defined by a name, a default value and a description.

The monitoring tab allows you to specify the monitoring of the pipeline.

The options to set in this tab are: