Day: February 1, 2019

Let’s discuss here what all the different ways we can able to use the wire services in the lightning web component world. To read Salesforce data, Lightning web components use a reactive wire service, which is built on Lightning Data Service. Components use @wire in their JavaScript class to read data from one of the wire adapters in the lightning/ui*Apimodules and also to call the apex controller server-side methods using wire services.  The wire service provisions an immutable stream of data to the component. Each value in the stream is a newer version of the value that precedes it.

We call the wire service reactive in part because it supports reactive variables, which are prefixed with $. If a reactive variable changes, the wire service provisions new data. We say “provisions” instead of “requests” or “fetches” because if the data exists in the client cache, a network request may not be involved. The wire service delegates control flow to the Lightning Web Components engine. Delegating control is great for read operations, but it isn’t great for create, update, and delete operations. As a developer, you want complete control over operations that change data. That’s why you perform create, update, and delete operations with a JavaScript API instead of with the wire service.

Import References to Salesforce Objects and Fields

For Example, importing an object using a wire adapter it looks like below

To import a reference to a field, use this syntax.

For Example, importing a Field using wire adapter it looks like below.

To import a reference to a field via a relationship, use this syntax. You can specify up to 5 levels of spanning fields.

For Example, importing the relationship fields looks like as shown below .

The following code imports the Account.Name field and uses it in a wire adapter’s configuration object. When we call this code the wire service get the data from the Salesforce  account object which is similar like below SOQL “Select Id,Name from Account Where Id=’001xxxx”

Mark a Configuration Object Property as Dynamic and Reactive

In the wire adapter’s configuration object, prefix a value with $ to reference a property of the component instance. The $prefix tells the wire service to treat it as a property of the class and evaluate it as this.propertyName. The property is reactive. If the property’s value changes, new data is provisioned and the component rerenders.The following example get the contact record data using the wire service

Decorate a Property with @wire

Wiring a property is useful when you want to consume the data or error as-is. If the property decorated with @wire is used as an attribute in the template and its value changes, the wire service provisions the data and triggers the component to rerender. The property is private, but reactive, like a property decorated with @track.This code applies @wire to the record property.

Wiring a function is useful to perform logic whenever new data is provided or when an error occurs. The wire service provisions the function an object with error and data properties, just like a wired property. The function is invoked whenever a value is available, which can be before or after the component is connected or rendered.

Call Apex Methods using wire service 

Lightning web components can import methods from Apex classes. The imported methods are functions that the component can call either via @wire or imperatively. For example, to return a simple list of accounts, it would be best to use getListUi. But to use a SOQL query to select certain accounts, you have to use an Apex method. When an Apex class name changes outside of the JavaScript source file, the class name is automatically updated in the JavaScript source file. Method and argument name changes aren’t updated in the JavaScript source file.

The below JavaScript code imports the Apex method and invokes it via the wire service. The wire service either provisions the list of contacts to the contacts.data property, or returns an error to the contacts.error property using the wire property .

The below JavaScript code imports the Apex method and invokes it via the wire service. The wire service provisions the results to the wiredContacts() function via an object with either an error or data property. If the wire service provisions data, it’s assigned to this.contacts, which is tracked and used in the template. If it provisions error, it’s assigned to this.error, which is also tracked and used in the template. If the value of a tracked property changes, the template rerenders.

Using lightning/ui*Api Wire Adapters

Wire adapters and JavaScript functions in these modules are built on top of Lightning Data Service (LDS) and User Interface API. Use these wire adapters and functions to work with Salesforce data and metadata . Here is are the some of the useful wire adapters

getListUi

Use this wire adapter to get the records and metadata for a list view . For Example, the following wire adapter gets the allaccounts list view data.

getRecord