Understanding Salesforce Files and Efficient Querying

Introduction

Salesforce stores files using several key objects: ContentVersion, ContentDocument, ContentDocumentLink, ContentDocumentFeed, and ContentDocumentHistory. However, in most use cases, we primarily work with the first three—ContentVersion, ContentDocument, and ContentDocumentLink.

What Are These Objects?

• ContentDocument: Represents the actual file stored in Salesforce.
• ContentVersion: Represents a specific version of the file.
• ContentDocumentLink: Links the file to related records (e.g., Account, Contact).

Relationship Among These Objects

• A ContentDocument can have multiple ContentVersion records.
• The LatestPublishedVersionId field on ContentDocument helps retrieve the latest version.
• ContentDocumentLink connects a file to a record, enabling retrieval of related files.

Efficient vs. Inefficient Querying

Inefficient Approach

If you want to retrieve ContentVersion details of a record, a common but inefficient approach is:

List<ContentVersion> contentVersionList = new List<ContentVersion>();
List<ContentDocumentLink> contentDocumentList = [SELECT ContentDocumentId, LinkedEntityId FROM ContentDocumentLink WHERE LinkedEntityId =: recId];

if (!contentDocumentList.isEmpty()) {
    Set<Id> contentDocumentId = new Set<Id>();
    
    for (ContentDocumentLink cdl : contentDocumentList) {
        contentDocumentId.add(cdl.ContentDocumentId);
    }
    
    contentVersionList = [SELECT Id, VersionData, FileType, Title, FileExtension, 
        ContentDocument.CreatedBy.Name, ContentDocument.ContentSize, CreatedDate, 
        ContentDocumentId, ContentDocument.FileType, Public_URL__c 
        FROM ContentVersion WHERE ContentDocumentId IN : contentDocumentId];
}

This approach involves multiple queries, making it inefficient.

Efficient Approach

Instead, we can optimize the query by leveraging LatestPublishedVersion in ContentDocument:

List<ContentDocumentLink> contentDocumentList = [SELECT ContentDocumentId, 
    ContentDocument.LatestPublishedVersion.Id, 
    ContentDocument.LatestPublishedVersion.VersionData, 
    ContentDocument.LatestPublishedVersion.FileType, 
    ContentDocument.LatestPublishedVersion.Title, 
    ContentDocument.LatestPublishedVersion.FileExtension, 
    ContentDocument.CreatedBy.Name, 
    ContentDocument.ContentSize, 
    ContentDocument.LatestPublishedVersion.CreatedDate, 
    ContentDocument.FileType, 
    ContentDocument.LatestPublishedVersion.Public_URL__c, 
    ContentDocument.LatestPublishedVersion.Print_Status__c, 
    LinkedEntityId 
    FROM ContentDocumentLink 
    WHERE LinkedEntityId =: recId 
    ORDER BY ContentDocument.LatestPublishedVersion.Title];

Here, LinkedEntityId represents the record (e.g., Account, Contact) linked to the files.

Conclusion

When working with Salesforce files, always use ContentDocumentLink to efficiently retrieve ContentVersion and ContentDocument data in a single query. This reduces unnecessary queries and improves performance.