Accessing info from CommonPart is extremely slow?

问题

I'm new to Orchard and this must be something involving how the underlying data is stored.

The joining with CommonPart seems fast enough, like this:

var items = _contentManager.Query<MyUserPart, MyUserPartRecord>("someTypeName")
                           .ForVersion(VersionOptions.Published)
                           .Join<CommonPartRecord>().List().ToList();

That runs fairly fast. But whenever I try accessing some field in CommonPart, it runs extremely slow like this:

var items = _contentManager.Query<MyUserPart, MyUserPartRecord>("someTypeName")
                           .ForVersion(VersionOptions.Published)
                           .Join<CommonPartRecord>().List()
                           //access some field from commonpart
                           .Select(e => new {                               
                               User = e.As<CommonPart>().Owner.UserName
                            }).ToList();

The total data is just about 1200 items, and the time it needs is about 5 seconds, it cannot be slow like that. For a simple SQL query run in background, it should take a time of about 0.5 second or even less than.

I've tried investigating the Orchard's source code but found nothing that could be the issue. Everything seems to go into a blackbox at the accessing point of IContent. I hope someone here could give me some suggestion to diagnose and solve this hard issue. Thanks!

Update:

I've tried debugging a bit and seen that the following method is hit inside the DefaultContentManager:

ContentItem New(string contentType) { ... }

Well that's really interesting, the query is just asking for data without modifying, inserting and updating anything. But that method being hit shows that something's wrong here.

Update:

With @Bertrand Le Roy's comment, I've tried the following codes with QueryHint but looks like it does not change anything:

var items = _contentManager.Query<MyUserPart, MyUserPartRecord>("someTypeName")
                           .ForVersion(VersionOptions.Published)
                           .Join<CommonPartRecord>()
                           .WithQueryHints(new QueryHints().ExpandParts<CommonPart>())
                           .List()
                           //access some field from commonpart
                           .Select(e => new {                               
                               User = e.As<CommonPart>().Owner.UserName
                            }).ToList();

and this (without .Join)

var items = _contentManager.Query<MyUserPart, MyUserPartRecord>("someTypeName")
                           .ForVersion(VersionOptions.Published)
                           .WithQueryHints(new QueryHints().ExpandParts<CommonPart>())
                           .List()
                           //access some field from commonpart
                           .Select(e => new {                               
                               User = e.As<CommonPart>().Owner.UserName
                            }).ToList();

回答1:

Accessing the Owner property from your Select causes the lazy loader in CommonPartHandler to ask the content manager to load the user content item: _contentManager.Get<IUser>(part.Record.OwnerId). This happens once per content item result from your query, so results in a select n+1 where n = 1200 according to your question.

There are at least two ways of avoiding that:

You can use HQL and craft a query that gives you everything you need up front in 1 operation.
You can make a 1st content manager query to get the set of owner ids, and then make a second content manager query for those Ids and get everything you need with a total of 2 queries instead of 1201.

来源：https://stackoverflow.com/questions/55507342/accessing-info-from-commonpart-is-extremely-slow

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