/**
* This method allows for a concurrency-safe pattern to check for the existence of a given entity and, if it
* does not exist to create it, or if it does exist, to update it.
*
* This is concurrency-safe as it ensures that any two concurrent importer processes that are trying to create
* or update the same entity type with the same ID will not be able to do so at the same time. Rather, the
* first thread to reach this code will acquire a lock and prevent the second thread from being able to check
* for the existence of the entity until the first thread has finished creating it. At this point, the second
* thread is freed up to check if the entity already exists, which by this point, it will.
*/
private Task <TEntity> CreateOrUpdateWithExclusiveLock <TEntity, TMessageObject>(
string entityName,
StatisticsDbContext statisticsDbContext,
TMessageObject objectFromMessage,
Guid entityId,
TEntity entityToCreate)
where TEntity : class
where TMessageObject : class
{
var typeName = typeof(TEntity).Name;
return(DbUtils.ExecuteWithExclusiveLock(
statisticsDbContext,
$"CreateOrUpdate{typeName}-{entityId}",
async(context) =>
{
_logger.LogInformation(
$"Checking for existence of {typeName} \"{entityName}\"");
var existing = await statisticsDbContext.Set <TEntity>().FindAsync(entityId);
if (existing == null)
{
_logger.LogInformation($"Creating {typeName} \"{entityName}\"");
TEntity created = (await statisticsDbContext.Set <TEntity>().AddAsync(entityToCreate)).Entity;
await statisticsDbContext.SaveChangesAsync();
return created;
}
_logger.LogInformation($"{typeName} \"{entityName}\" already exists - updating");
TEntity mappedEntity = _mapper.Map(objectFromMessage, existing);
TEntity updated = statisticsDbContext.Set <TEntity>().Update(mappedEntity).Entity;
await statisticsDbContext.SaveChangesAsync();
return updated;
}));
}
protected DbSet <TEntity> DbSet()
{
return(_context.Set <TEntity>());
}
