Скачать или смотреть Resolving the ERROR Error: Error trying to diff '[object Object]' in Angular's NgFor

Discover how to fix the common `ERROR Error: Error trying to diff '[object Object]'` in Angular when looping through an array with NgFor, by correctly accessing nested properties.
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This video is based on the question https://stackoverflow.com/q/67723640/ asked by the user 'Jonald Monday' ( https://stackoverflow.com/u/9476256/ ) and on the answer https://stackoverflow.com/a/67723795/ provided by the user 'NeNaD' ( https://stackoverflow.com/u/14389830/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the ERROR Error: Error trying to diff '[object Object]' in Angular's NgFor

When working with Angular, especially with NgFor, encountering errors related to data structure can be frustrating. One common issue is the error message: ERROR Error: Error trying to diff '[object Object]'. Only arrays and iterables are allowed. This typically arises when trying to loop over objects or incorrectly structured data. In this guide, we'll break down what this error means and how to fix it effectively.

The Problem

While attempting to build a certificate table using data retrieved from an API, the developer faced the following error message:

[[See Video to Reveal this Text or Code Snippet]]

Upon inspecting the API's response, it became clear that the response structure does not directly match the expected format needed by NgFor. The returned object has a value property that contains the array of certificates, but the component attempts to access certificates directly from the general object.

Understanding the API Response

The following is the structure of the API response:

[[See Video to Reveal this Text or Code Snippet]]

Key Takeaways from the API Response:

The main object has a property called value which is an array containing certificate objects.

Each certificate object has a properties field among others like id, name, and type.

The Solution

To correctly display the certificates, adjustments must be made both in how the data is assigned in the component and how it is rendered in the template. Here’s a step-by-step guide on implementing these changes.

Step 1: Updating the Component

Ensure that you are accessing the value property from the API response when assigning data to listcertificates. Your updated component should look like this:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Updating the Template

Modify the template to correctly iterate over the value property within listcertificates. You can use an *ngIf to guard against null values. Here is how your table structure should look:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Made:

*ngIf Guard: It checks whether listcertificates, listcertificates.value, and the length of the value array exist. This prevents the table from trying to render when no data is available yet, avoiding further errors.

Iterating Over Array: By accessing listcertificates.value, we ensure that we are looping through an actual array.

Conclusion

By carefully inspecting the structure of the API response and making the necessary updates in both the Angular component and template, you can resolve the common error related to using NgFor with incorrect data types. Always remember to verify the data structure that you are working with in your Angular applications, as this will save you time and effort in debugging. Happy coding!