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azure-cosmosdb

Cosmos DB image/file attachment

I have created a document with pdf attachment using below code and it's working (able to retrieve attached file).

var myDoc = new { id = "42", Name = "Max", City="Aberdeen" }; // this is the document you are trying to save
var attachmentStream = File.OpenRead("c:/Path/To/File.pdf"); // this is the document stream you are attaching

var client = await GetClientAsync();
var createUrl = UriFactory.CreateDocumentCollectionUri(DatabaseName, CollectionName);
Document document = await client.CreateDocumentAsync(createUrl, myDoc);

await client.CreateAttachmentAsync(document.SelfLink, attachmentStream, new MediaOptions()
{
    ContentType = "application/pdf", // your application type
    Slug = "78", // this is actually attachment ID
});

I can upload a document directly in blob storage and put that blob URL in the document.

Can anyone help me to understand the value of inbuild attachment feature? how this is better than blob and other option? where cosmos DB keep attachment?

I want to understand which scenario we should consider this option (I know 2GB per account limitation)

Solution

  • Can anyone help me to understand the value of inbuild attachment feature?how this is better than blob and other option?

    Based on this official doc, you could get answer for your question.

    You could store two types data:

    1.binary blobs/media

    2.metadata (for example, location, author etc.) of a media stored in a remote media storage

    In addition,attachments has garbage disposal mechanism which is different with Azure Blob Storage I think.

    Azure Cosmos DB will ensure to garbage collect the media when all of the outstanding references are dropped. Azure Cosmos DB automatically generates the attachment when you upload the new media and populates the _media to point to the newly added media. If you choose to store the media in a remote blob store managed by you (for example, OneDrive, Azure Storage, DropBox, etc.), you can still use attachments to reference the media. In this case, you will create the attachment yourself and populate its _media property.

    So,per my understanding,if your resource data will be frequently added or deleted, I think you could consider using attachment. You just need to store remote URL into _media property.

    where cosmos DB keep attachment?

    Attachment is stored in the collection as JSON format document,it can be created, replaced, deleted, read, or enumerated easily using either REST APIs or any of the client SDKs. As I know, it can't display on the portal so far.

    BTW, Azure cosmos db is more expensive than blob storage usually.I think cost is an important factor to consider. More details, you could refer to the price doc.

    Hope I'm clear on this.