Custom GROQ Request in Sanity Preview/Prepare Functions

Yes, you can access the original filename and other asset metadata in your preview configuration! The key is to use dot notation to dereference the image asset in your select object. Instead of just selecting image, you need to select image.asset and then the specific fields you want from the asset document.

Here's how to modify your code to get the original filename:

export default {
    name: 'singleImage',
    title: 'Single image',
    type: 'object',
    fields: [
        {name: 'image', type: 'image'}
    ],
    preview: {
        select: {
            image: 'image',
            originalFilename: 'image.asset->originalFilename',  // Use -> to dereference
            extension: 'image.asset->extension',
            url: 'image.asset->url'
        },
        prepare: ({image, originalFilename, extension, url}) => {
            console.log('Original filename:', originalFilename);
            console.log('Extension:', extension);
            return {
                title: originalFilename || 'Single image',
                subtitle: extension ? `${extension.toUpperCase()} file` : undefined,
                media: image
            }
        }
    }
}

The -> operator is the dereference operator in Sanity's select syntax. When you use image.asset->originalFilename, you're telling Sanity to:

1. Get the image field
2. Follow the reference in image.asset
3. Retrieve the originalFilename field from the referenced asset document

This works because image assets in Sanity are stored as separate documents in the sanity.imageAsset type, which includes fields like:

• originalFilename - The original name of the uploaded file
• extension - File extension (jpg, png, etc.)
• url - The asset URL
• metadata - Contains dimensions, palette, etc.

You can also access nested metadata like dimensions:

select: {
    image: 'image',
    originalFilename: 'image.asset->originalFilename',
    width: 'image.asset->metadata.dimensions.width',
    height: 'image.asset->metadata.dimensions.height'
}

Important limitation: As mentioned in the preview configuration documentation, the prepare function cannot make custom GROQ queries. All data fetching must happen in the select object using this dot notation and dereference syntax. The prepare function only transforms the data that was already selected.