Angular: Reactive Form setValue v/s patchValue

In Angular, setValue() and patchValue() are methods used to update the values of form controls in reactive forms. Here’s when to use each:

setValue()

• Use When: You need to set all the values for the form controls.
• Behavior: It requires that the object you pass matches the structure of the form group or form array exactly. If any control is missing, it will throw an error.
• Example:

  this.form.setValue({
    firstName: 'John',
    lastName: 'Doe',
    age: 30
  });

In this example, the form must have controls for firstName, lastName, and age. If any of these are missing, setValue() will throw an error.

patchValue()

• Use When: You need to update only some of the values for the form controls.
• Behavior: It allows you to pass an object with a subset of the form group or form array values. It will only update the specified controls and leave the rest unchanged.
• Example:

  this.form.patchValue({
    firstName: 'John'
  });

In this example, only the firstName control is updated. The other controls (lastName and age) remain unchanged.

Summary

• setValue(): Use when you need to set all form controls and the object structure must match the form structure exactly.
• patchValue(): Use when you need to update only specific form controls and the object structure can be a partial match.

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