protected internal async virtual Task <bool> TryUpdateIsLatestInDatabase(IEntitiesContext context)
{
// Use the EF change tracker to identify changes made in TryUpdateIsLatestAsync which
// need to be applied to the database below.
// Note that the change tracker is not mocked which make this method hard to unit test.
var changeTracker = context.GetChangeTracker();
var modifiedPackages = changeTracker.Entries <Package>().Where(p => p.State == EntityState.Modified).ToList();
if (modifiedPackages.Count == 0)
{
return(true);
}
// Apply changes to the database with an optimistic concurrency check to prevent multiple
// threads (in the same or different gallery instance) from setting IsLatest/IsLatestStable
// flag to true on different package versions.
// To preserve existing behavior, we only want to reject concurrent updates which set the
// IsLatest/IsLatestStable columns. For this reason, we must avoid the EF ConcurrencyCheck
// attribute which could reject any package update or delete.
var query = new StringBuilder("DECLARE @rowCount INT = 0");
foreach (var packageEntry in modifiedPackages)
{
// Set LastUpdated after all IsLatest/IsLatestStable changes are complete to ensure
// that we don't update rows where IsLatest/IsLatestStable hasn't changed.
packageEntry.Entity.LastUpdated = DateTime.UtcNow;
var isLatest = packageEntry.Entity.IsLatest ? 1 : 0;
var isLatestStable = packageEntry.Entity.IsLatestStable ? 1 : 0;
var key = packageEntry.Entity.Key;
var originalIsLatest = Boolean.Parse(packageEntry.OriginalValues["IsLatest"].ToString()) ? 1 : 0;
var originalIsLatestStable = Boolean.Parse(packageEntry.OriginalValues["IsLatestStable"].ToString()) ? 1 : 0;
query.AppendLine($"UPDATE [dbo].[Packages]");
query.AppendLine($"SET [IsLatest] = {isLatest}, [IsLatestStable] = {isLatestStable}, [LastUpdated] = GETUTCDATE()");
query.AppendLine($"WHERE [Key] = {key}");
// optimistic concurrency check to prevent concurrent sets of latest/latestStable
query.AppendLine($" AND [IsLatest] = {originalIsLatest} AND [IsLatestStable] = {originalIsLatestStable}");
// ensure new latest/latestStable was not concurrently unlisted/deleted
if (packageEntry.Entity.IsLatest || packageEntry.Entity.IsLatestStable)
{
query.AppendLine($" AND [Listed] = 1 AND [Deleted] = 0");
}
query.AppendLine($"SET @rowCount = @rowCount + @@ROWCOUNT");
}
query.AppendLine("SELECT @rowCount");
using (var transaction = context.GetDatabase().BeginTransaction(IsolationLevel.ReadCommitted))
{
var rowCount = await context.GetDatabase().ExecuteSqlCommandAsync(query.ToString());
if (rowCount == modifiedPackages.Count)
{
transaction.Commit();
return(true);
}
else
{
// RowCount will not match if one or more updates failed the concurrency check. This
// likely means another thread is trying to clear the current IsLatest/IsLatestStable.
transaction.Rollback();
return(false);
}
}
}
