This post covers LINQ to SQL and EF worry #4. That is:
LINQ to SQL and EF will write code that gets too much or too little data at a time. Too much data in one query is a waste. Too little data is also bad because it means extra database round-trips.
I really put this in for completeness. Both LINQ to SQL and EF have good mechanisms to deal with this one. In addition, its not necessarily (only) an ORM problem. In a file system graphic user interface, do you prefetch all of the (perhaps thousands) or files' information throughout the entire file system when someone wants to look at the content of the C drive? The answer with this one is "it depends". If you know you're going to eventually display all of the related entities' information you likely do want to get them. If not, perhaps you want to get related entities all at one, when the first child entity is selected. Or get the children one at a time when each child entity is selected.
LINQ to SQL addresses this by implementing a property on the DataContext, the DeferredLoadingEnabled property. It is True by default, retrieving only the Customer object when the Customer has Orders. The related Orders objects are retrieve with an extra roundtrip to the database, one row at a time, when the Customers' Orders property is accessed in code. There is a related property, LoadOptions, on the DataContext that takes a DataLoadOptions instance that allows you to control exactly how much related data is retrieved. That is, do I want only related Orders or Orders, OrderDetails, and associated Products in a single round trip? The DataLoadOptions also allows you to filter the amount of data you get from related tables, that is, I want each Customers' associated Orders, but only OrderID and OrderDate.
ADO.NET Entity Framework does this a little differently. They don't have a property for whether deferred loading is enabled, they just load deferred by default. In order to load associated entites, there is a separate Load method, and an IsLoaded property that you can check before loading. EF also has an Include property of the query of also you to specify which related entities can be loaded, if eager loading is desired. With EF you can also use Entity-Splitting in your design if you know you always want to retrieve OrderID and OrderDate, but no other properties, from the Orders table. Object purists may frown on composing object based only on commonly-used queries, however.
You can also retrieve only certain columns from an object (ie all the fields in Customers but the Customers' picture) with either a related or anonymous type. And, of course, you can always specify a join that returns an anonymous type is desired to get just the properties you need from related tables.
So I'd say that this worry not only is completely unwarrented, but that LINQ to SQL and EF make programmers think more about lazy loading vs eager loading, and make it clearer and more maintainable than a join, which always returns an "anonymous rowset" with columns from all tables interspersed. That is, you know exactly what related data (at an object level) is being requested and retrieved.
Sorry, comments are closed for this post.