A common mistake when you start with Qlik Sense extensions is to forget about setting Initial data fetch in your extension. Typically you would include something like this in the initialProperties of your extension:
That would work, and make sure your extension gets the 500 first rows of data in the layout provided to your paint method. But sometimes you want the app developer to be able to set the number of rows fetched. In that case you can simply add the qHeight parameter to the property panel like this:
And the result is a new section in the property panel, where the app developer can set the number of rows initially fetched.
The property panel is a key part of your Qlik Sense extension. The aibility to set extension properties is what makes your extension both reusable and flexible. At the same time your options are much more limited than in the rendering part of the extension. And since this is Qlik Sense specific all of it, there is not so much information and examples available on the internet. So here are some patterns and techniques I find useful in extension development.
1. Use expressions always
Strings in the property panel can allow Qlik Sense expression by setting “expression: ‘optional’ “. Use that – always. This allows the app developer to use expressions for the property and thereby make the property dynamic. It also allows the app developer to reference a variable and use a variable extension to allow the end user to switch values for the property (horizontal/vertical for example).
It allows the app developer to use an expression, but doesn’t force her. Still a fixed string can be used, and probably will be used. And the good thing thing is you don’t have to bother about that in your extension code, you get this flexibility for free.
2. Dropdown with custom alternative
Sometimes you have just a few possible values for a property, or you want to help the app developer with a list of common values for a property. The dropdown component is a good choice for that. But you risk loosing the flexibility of the expression: the dropdown will only make it possible to select a value at design time, no possibility to make it dynamic or affected by a variable. Or the list is really not a complete list, there are alternatives for the more advanced app developer.
In those scenarios you can combine a dropdown with a separate field that allows expressions like this:
create a dropdown with your alternatives
add a ‘custom’ alternative to the dropdown
add a field with expression: ‘optional’ for the custom value
give the field a show function, that returns true if the selected value is ‘custom’
In your extension code you will need to check for custom values, something like this:
var width = layout.width === ‘custom’ ? layout.customwidth : layout.width;
3. Add properties to dimensions and measures
Sometimes you need a property for every dimension or measure. In that case you can extend the built-in dimensions and measures objects by adding new properties. You do this simply by setting the items property to the properties you want to add, and Qlik Sense will merge the default properties with the ones you hav defined. An example:
Note that the ref should begin with ‘qDef.’. That will mean it will be part of the measures property. To the app developer your roperty will look just like the built-in ones. You can do the same thing with dimensions.
One of the more advanced feature in QlikView is alternate state. It alllows you to have several different selections active at the same time. With set analysis expressions you can then combine your selection sets to gain valuable insights.
While alternate states are not exposed in the built-in Qlik Sense client, you can easily add them to your custom extension with just a few lines of code. Let’s see how.
Step 1: add a property panel field
The qStateName property already exists (check the Qix Engine API), so a first step is to map it to the property panel. Lets create a new section under “Addons”:
This assumes a HyperCube, $ is the default state which is always there. This is already enough for alternate state to work in your extension. If you enter a valid alternate state name in the property panel your extension will be connected to it. Problem is there has to be an alternate state in the app, and you need to know it’s name. Lets do something about that.
Step 2: add a listbox with existing alternate states.
Lets convert our property panel to a dropdown list, where the app developer can choose what state the object should be connected to. We do this by setting the component to ‘dropdown’ and adding a function to return the options:
Alternate states ar listed in the app layout structure, so we need to get the app layout and format the states in the format the property panel dropdown wants. The default state ‘$’ is not in the list, so we need to add that ourselves. For this to work you need to have the qlik module available in your extension.
Now you will have a dropdown list in your extension property panel, something like this:
Still doesn’t look much, does it… But it does it’s job. Now we just need a way to create those alternate states.
Step 3:Creating the alternate states
Well, actually you need to do this first. But there are different ways to achieve this:
there are extensions for this
you could do it in Engine API explorer, since its really a one-time thing
or, you could add it to the property panel.
The property panel is not really meant for this, since we are not updating the object properties, but the app properties, but still it’s pretty easy to do. You can add something like this to the property panel:
It’s really not more complicated than that. You will get an inputfield in the propertypanel. If the user writes anything in that field, an alternate state will be created. It will then show up in the listbox, so you can use it in your extension.
It’s really not at all difficult to add alternate state support to your extension. Probably you should do something to show the user that this chart belongs to an alternate state: you can use the header for that, or add some styling or an icon for charts that are in another state. I’ll leave that for you.
Probably the most important object you can have in your Generic Object is the HyperCube. It is what is used in most charts and is the way to tap into engine associative logic and calculation engine. Hypercubes reflect the users selections and calculations will be made on the current selections.
The hypercube properties are in a structure called qHyperCubeDef. A common setup is the one from the peoplechart extension example we have seen before:
This will create a hypercube definition with an empty array of dimensions and an empty array of measures. It will also tell engine to include 2 columns (probably 1 dimension and 1 measure) and 50 rows of data with the initial fetch of data, that is in the reply to the getLayout call. This works because the user can add dimensions and measures using the property panel, which is defined like this:
In a mashup you would in most cases need to list the dimensions and measures you want, something like this (taken from my angular-based mashup example available on GitHub:
This will create a hypercube with eight dimensions and no measures, tell engine that we want all eight columns and 400 rows in the initial fetch, set some other properties and define a call back function called setCases (not included above) that will be called every time the hypercube data has changed.
While it is possible to have a hypercube without dimensions, you probably could use a simple expression instead in most cases. So you normally would have a dimension array. This array should contain one or more NxDimenion object(found here, you need to scroll down a bit). There are two alternatives:
use a predefined dimension from the list of dimensions. If you do that you should set the qLibraryId to the id of the dimension you want to use.
use a dimension that is defined only in this dimension array. In that case you should set qDef to an object that in turn contains the dimension definition. Note that qFieldDefs is actually an array, and so can contain multiple definitions. You can actually define a cyclic group here, though I have never seen it used and don’t think it is supported in the client.
Whether you use a predefined dimension or a locally defined dimension there are some additional properties that might be useful. The most complicated is qOtherTotalSpec, which you can use to limit your hypercube to the top 10 values, or bottom 10 etc.
The measures array works much like the dimensions array. It also has two alternatives: referring to a predefined mease with the qLibraryId field or defining the expression in a qDef structure. Note that the measure qDef structure is not the same as the dimension qDef structure: instead of the qFieldDefs array it holds just a string field (also named qDef) with the actual expression.
Make sure you get some rows
To make sure you actually get some data in your hypercube you need to set the qInitialDataFetch property. This is actually an array, but I have never seen an example with more than one entry in the array. You should set qWidth to the number of columns (that is dimensions plus measures) in your cube and qHeight to the number of rows you need for the initial rendering of your cube.
If you do not set this property, the default is 0 rows and 0 columns, so you will get no data. A very common problem in extension development is that you add dimensions or measures and forget to update the qWidth parameter, so you do not get any values for your measures. Also rememeber that what you specify in your extension is the initial properties, so when you change your code, the objects already created will not change. A way to avoid this problem is to set qWidth to something high (10, for example) since a value that is higher than the actual number of columns will work and get you all columns.
Create a hypercube in the mashup editor
A feature not well known in Qlik Sense mashup editor is that it can help you create a hypercube. In the left column of the editor there is a button labeled ‘Add hypercube’. Select the app you want to work with and click it, and you will get a popup, something like this:
When you click the ‘Add’ button, it will create a createCube call for you, with most of the properties filled in:
Even if you don not use the mashup editor for creating your mashup, this feature can be useful.
Getting data out of a Qlik Sense app is based on a concept called Generic Object. Behind all charts, tables and listboxes in Qlik Sense lies a generic object. Also behind many of the other things you see in the Qlik Sense client lies generic objects:
the selection toolbar
the panel on the left side of the page, with lists of dimensions, measures and master objects
the sheet is a generic object
The purpose of the Generic Object is to make it easier to make client-side changes without having to change the QIX engine. Since the Generic Object is very flexible, many client side changes do not require any changes to the engine. This is in contrast to how it works in QlikView, where all charts have different server-side implementations and client and server code are tightly coupled. This is also a reason why extensions are so powerful in Qlik Sense: to the QIX engine there is really no difference between built-in visualizations and extensions, they are all represented with a Generic Object.
Properties and layout
When you create a Generic Object you define its properties. This is a JSON structure, which you can define yourself. An example (from the peoplechart extension example):
There are two kind of properties:
user defined. Qlik only persists those and include them as-is in the layout, it is up to your code to use them for something
defined by Qlik Engine. These are validated by the Engine, and replaced in Engine output, the layout, by the calculated counterparts.
All properties defined by Engine start with a q, so it is good programming practice to let your own properties start with some other letter. The properties defined by Engine are documented here and the corresponding out data is documented here. Note that properties defined by the Qlik Sense client(like title etc) do NOT start with a q, the QIX engine does not really know what these are used for.
But the parameters known by the QIX Engine will determine the engines calculation. In the output from engine, called layout (though it’s not really the layout of a Generic Object) the definition of those properties will be replaced by the results. A hypercube definition (qHyperCubeDef) will be replaced by a actual hypercube (qHyperCube) containing the results from the calculation.
Generic Object context
Generic objects are everywhere in Qlik Sense. If you are building an extension, you define your Generic Object structure in the initialProperties property. If you are using the mashup API, you create generic objects with the createGenericObject method or one of the wrappers around it (createCube, createList, getList). In both these cases the Qlik Sense client framework will automatically refresh the Generic object with new data when it is invalidated (by for example new selections). If you are working directly on the protocol level, you need to fetch they new data yourself.