Collections
In the previous two units, you learned how global and contextual variables store single values. The third variable type, collections, allow you to store a table of data. This is ideal when you need to store large amounts of structured data for reuse in your app. This data can come directly from a data source, can be created within the app, or a combination of both.
Using collections to increase performance
The most common reason for using collections is to optimize performance by reducing calls to the same table in a data source. For example, if you have a table that stores all of your active projects and you want to reference that list multiple times in your app, then you should consider querying for that data once and storing it in a collection. To store a copy of the Projects table from your data source into a collection called collectProjects, use the following formula.
Collect(collectProjects, Projects)
This will create a collection named collectProjects that will have the same rows and columns as the Projects table from your data source. Here is a couple of considerations that you need to understand about using collections:
The Collect function is not delegable. This means by default only the first 500 records from the data source will be retrieved and stored in the collection. For more information about working with delegation, see Work with data source limits (delegation limits) in a Power Apps canvas app
Collections are not linked to the data source after you create them. This means changes to the data in the collection do not automatically save to the data source. This includes changes you have made to the data. If you want to update the data source based on your changes to the collection, you will need to build formulas to do so, such as recollecting from the data source.
Collections are temporary. When you close the app, the collection and all of its contents are removed. If you need to store collection data, you need to write it to a data source before closing the app.
Using dynamic collections
Collections do not have to come from a data source. You can also create a collection from information directly within your app. This is often done to provide values for a drop-down menu or combo box and to store large amounts of data before writing to a data source.
Creating a collection with your own data is similar to working with the other variable types. The following formula will create a collection named collectColors that matches the structure shown in the following table.
Collect(collectColors, {Name: "Shane", FavoriteColor: "Orange"},
{Name: "Mary", FavoriteColor: "Blue"}, {Name: "Oscar", FavoriteColor:
"Yellow"})
| Name | FavoriteColor |
|---|---|
| Shane | Orange |
| Mary | Blue |
| Oscar | Yellow |
After you create the collection, you can then reuse it throughout your app. This also means all of the table functions are available to be used. The one exception where Collections vary from tabular data sources is you cannot use them with the Form control.
For more information about working with collections and the table data they store, see Author a basic formula that uses tables and records in a Power Apps canvas app.
Additionally, collections store table data no differently than tabular data sources. The learning path Work with data in a Power Apps canvas app has many concepts that allow you to work with and extend the power of your collections.
In the final unit of this module, you will learn about some additional variable concepts and how to apply them to your apps.