How to update meta fields of multiple posts in WordPress using a single REST request

Building a custom settings page in WordPress using React, I faced the situation where I wanted to update meta fields of multiple posts at once. I want to share the approach I used with the WordPress REST API.

The WordPress REST API has a framework for making a series of REST API calls at once. It is handy to update meta fields of multiple posts using a single REST request. The framework name is REST API Batch Framework. Next are the steps I took to use it.

Registration of the meta fields in the REST API

First I registered the custom meta field in the REST API using the register_post_meta function.

add_action( 'init', function() {
	register_post_meta(
		'post',
		'my_custom_field_name',
		[
			'single'       => true,
			'type'         => 'string',
			'show_in_rest' =>  true,
		]
	);
} );

• The first argument I used here is 'post', which means that the custom field is applied for items saved in the posts table (posts, pages and custom post types). Here you can use other entities like 'comment', 'term' or 'user'. If the meta field is used in a custom post type, then the custom post type should support custom fields. During the custom post type registration, you can use the supports field to add custom-fields.
• The second argument is 'my_custom_field_name' which is the key name used for the meta field.
• The last argument describes the meta field. In this example, the meta field has one value per post only, its type is string and its value is accessible via the REST API. Indeed, the value of the 'show_in_rest' key can be an array with the key 'schema' to describe its data structure in the REST API.

Using the Batch Framework to update meta fields of multiple posts in WordPress

The React component uses the Batch Framework and it is in charge of doing the request to update the posts. It has a function to update the meta fields of multiple posts in WordPress using a single request. The request looks like this:

const requests = [
	{
		path: '/wp/v2/posts/10',
		method: 'POST',
		body: {
			meta: {
				my_custom_field_name: 'hello world',
			},
		},
	},
	{
		path: '/wp/v2/posts/11',
		method: 'POST',
		body: {
			meta: {
				my_custom_field_name: 'lorem ipsum...',
			},
		},
	},
	{
		path: '/wp/v2/posts/12',
		method: 'POST',
		body: {
			meta: {
				my_custom_field_name: '123abc',
			},
		},
	}
];
apiFetch( {
	path: 'batch/v1',
	method: 'POST',
	data: { requests },
} )
	.then( response => handleBatchResponse( response, requests ) )
	.catch( err => console.log( err ) );

The apiFetch call use the next config object:

• The path and the method properties of the Batch Framework endpoint, batch/v1 and POST respectively.
• The data property is an object with the property requests which contains an array with the configuration of each one of the requests we want to execute. Each configuration is an object with the required property path and optionally the properties method, headers and body. In this case, these are the configuration to make the requests to the WordPress endpoint POST /wp/v2/posts/<id> to update the posts.

Handling the response

Finally here is how to handle the response of the request to update meta fields of multiple posts in WordPress. In the React component, I defined the next function:

const handleBatchResponse = ( batchResponse, requests ) => {
	batchResponse.responses.forEach( ( requestResponse, idx ) => {
		// Get the data of the request related to the current response.
		const requestData = requests[ idx ];

		// Check if the response was not successful.
		if ( 200 !== requestResponse.status ) {
			// Show error message here.
		}
	} );
} );

The custom function handleBatchResponse expects 2 parameters, the response of the batch request and the array of requests sent in the batch request. This function is called when the response of the request is received and parsed by the apiFetch call. The response of the batch requests is an object with the property responses which is an array of enveloped responses objects for each one of the requests sent in the batch request. Each enveloped response has the properties status, headers and body. The order of the items in the responses array corresponds to the order of the items in the requests array sent in the batch request, so the first object in batchResponses.responses is the response of the first object in the requests array.

Conclusion

It is possible to update meta fields of multiple posts in WordPress using a single REST requests. The REST API Batch Framework allows to run multiple requests at once in WordPress. However, take into account that it accepts up to 25 requests in a single batch. Additionally, the framework doesn’t support GET requests. Using parallel requests or linking and embedding are the recommendation in this case.