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2012-09-07T19:17:48.683
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When quering over multiple child collections using NHibernate, I tend to prefer to use the LINQ query syntax over lambdas because not only is it much easier to write but the code looks cleaner. Take this example which should point you in the right direction: <pre><code>var listOfString = new List<string>() { "String1", "String2" }; var customers = ( from a in session.Query<A>() from b in a.B from c in b.C where a.Status == "Active" && listOfStrings.Contains( b.SomeField ) && listOfStrings.Contains( c.someOtherField ) select a ) .ToList(); </code></pre> By using the LINQ query syntax, we can easily add multiple FROMs to gain access to the child collections. Then it's just a matter of apply your WHERE conditions. For your particular case, you would simply use LINQ's Contains() method which equates to SQL's IN operator. It also sounds like you are wanting to load all the child collections into memory as well so be sure to use NHibernate's .Fetch() method to eagerly load that data like so: <pre><code>var customers = ( from a in session.Query<A>() from b in a.B from c in b.C where a.Status == "Active" && listOfStrings.Contains( b.SomeField ) && listOfStrings.Contains( c.someOtherField ) select a ) .Fetch( x => x.B ) .ThenFetchMany( x => x.First().C ) .ToList(); </code></pre> FYI, using the .First() inside the .ThenFetchMany() method above is a trick I learned from the NHibernate's Jira issue tracker website: <a href="https://nhibernate.jira.com/browse/NH-2972?focusedCommentId=22150&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-22150" rel="nofollow">https://nhibernate.jira.com/browse/NH-2972?focusedCommentId=22150&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-22150</a>
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1. POHow to efficiently query with filter on children at different levels?
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1. COAbsolutely beautiful answer - thank you! I am just getting started with FNH, but really liking it so far! Particularly all the help here on SO.
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Querying!

Guidance

A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.