Apex DocumentLink Trigger to Share Documents to Community Contacts

Trigger to check if the custom object has the correct file shared to community user

public without sharing class Domain_Documents extends fflib_SObjectDomain {

	public Domain_Documents(List<Documents__c> records) {
		super(records);
	}

	public class Constructor implements fflib_SObjectDomain.IConstructable{
		public fflib_SObjectDomain construct(List<SObject> sObjectList){
			return new Domain_Documents(sObjectList);
		}
	}

	public override void onAfterUpdate(Map<Id,SObject> existingRecords){
		List<ContentDocumentLink> contentDocumentLinksList = new List<ContentDocumentLink>();
		for (Documents__c documents : (List<Documents__c>) Records){
			if (documents.File_Id__c!=null){
				Documents__c existingDocument = (Documents__c)existingRecords.get(documents.Id);
				if (existingDocument.File_Id__c==null){
					List<ContentDocumentLink> contentDocumentLinkExists = [select ContentDocumentId, Id, IsDeleted, LinkedEntityId, ShareType, SystemModstamp, Visibility from ContentDocumentLink where ContentDocumentId=:documents.File_Id__c];
					Id userToShareWith = [Select Client__r.User__c from Documents__c where Id=:documents.Id].Client__r.User__c;
					Boolean flagToAddToDocs = true;
					for (ContentDocumentLink contentDocumentLinkExist : contentDocumentLinkExists){
						if (contentDocumentLinkExist.LinkedEntityId==userToShareWith){
							flagToAddToDocs=false;
						}
					}
					if (flagToAddToDocs){
						ContentDocumentLink cdl = new ContentDocumentLink(LinkedEntityId = userToShareWith , ContentDocumentId=documents.File_Id__c, shareType = 'C');
						contentDocumentLinksList.add(cdl);
					}
				 }
             }
		}

		if (!contentDocumentLinksList.isEmpty()){
			insert contentDocumentLinksList;
		}
	}
}

Test class to check that sharing is done correctly

@isTest(SeeAllData=true) static void testUpdate() {
		User communityUser = Global_Test.setupCommunityUserAndLogin();

		Documents__c bpDocument = (Documents__c)SmartFactory.createSObject('Documents__c');
		bpDocument.OwnerId = communityUser.Id;
		bpDocument.File_Name__c='Test';
		bpDocument.Document_Status__c = 'New';
		bpDocument.Client__c = communityUser.ContactId;
		insert bpDocument;

		String yourFiles = 'Some file content here';

		ContentVersion conVer = new ContentVersion();
		conVer.ContentLocation = 'S'; // S specify this document is in SF, use E for external files
		conVer.PathOnClient = 'test.txt'; // The files name, extension is very important here which will help the file in preview.
		conVer.Title = 'Test file '; // Display name of the files
		conVer.VersionData = EncodingUtil.base64Decode(yourFiles); // converting your binary string to Blog
		conVer.NetworkId=[Select Id from Network where Status='Live'][0].Id; //current Live community, should just be 1 but could have many
		insert conVer;

		Id conDoc = [SELECT ContentDocumentId FROM ContentVersion WHERE Id =:conVer.Id].ContentDocumentId; //query for contentDocumentId
	 	ContentDocumentLink cDe = new ContentDocumentLink();
		cDe.ContentDocumentId = conDoc;
		cDe.LinkedEntityId = bpDocument.Id; // you can use objectId,GroupId etc
		cDe.ShareType = 'C';
		cDe.Visibility = 'AllUsers';
		insert cDe;

		bpDocument.File_Id__c = conDoc;
		update bpDocument;

		Test.startTest();
			System.runAs(communityUser){
				bpDocument.File_Name__c='Update Name of File';
				update bpDocument;
			}
		Test.stopTest();

		Documents__c queryBpDocuments = [Select Id, File_Name__c, Document_Type__c from Documents__c where Id=:bpDocument.Id][0];
		System.assertEquals(queryBpDocuments.File_Name__c, 'Update Name of File');
	}