.Include() vs .Load() performance in EntityFramework

Question

When querying a large table where you need to access the navigation properties later on in code (I explicitly don't want to use lazy loading) what will perform better .Include() or .Load()? Or why use the one over the other?

In this example the included tables all only have about 10 entries and employees has about 200 entries, and it can happen that most of those will be loaded anyway with include because they match the where clause.

Context.Measurements.Include(m => m.Product)                     .Include(m => m.ProductVersion)                     .Include(m => m.Line)                     .Include(m => m.MeasureEmployee)                     .Include(m => m.MeasurementType)                     .Where(m => m.MeasurementTime >= DateTime.Now.AddDays(-1))                     .ToList(); 

or

Context.Products.Load(); Context.ProductVersions.Load(); Context.Lines.Load(); Context.Employees.Load(); Context.MeasurementType.Load();  Context.Measurements.Where(m => m.MeasurementTime >= DateTime.Now.AddDays(-1))                     .ToList(); 

Answer 1

It depends, try both

When using Include(), you get the benefit of loading all of your data in a single call to the underlying data store. If this is a remote SQL Server, for example, that can be a major performance boost.

The downside is that Include() queries tend to get really complicated, especially if you have any filters (Where() calls, for example) or try to do any grouping. EF will generate very heavily nested queries using sub-SELECT and APPLY statements to get the data you want. It is also much less efficient -- you get back a single row of data with every possible child-object column in it, so data for your top level objects will be repeated a lot of times. (For example, a single parent object with 10 children will product 10 rows, each with the same data for the parent-object's columns.) I've had single EF queries get so complex they caused deadlocks when running at the same time as EF update logic.

The Load() method is much simpler. Each query is a single, easy, straightforward SELECT statement against a single table. These are much easier in every possible way, except you have to do many of them (possibly many times more). If you have nested collections of collections, you may even need to loop through your top level objects and Load their sub-objects. It can get out of hand.

Quick rule-of-thumb

Try to avoid having any more than three Include calls in a single query. I find that EF's queries get too ugly to recognize beyond that; it also matches my rule-of-thumb for SQL Server queries, that up to four JOIN statements in a single query works very well, but after that it's time to consider refactoring.

However, all of that is only a starting point.

It depends on your schema, your environment, your data, and many other factors.

In the end, you will just need to try it out each way.

Pick a reasonable "default" pattern to use, see if it's good enough, and if not, optimize to taste.

Answer 2

Include() will be written to SQL as JOIN: one database roundtrip.

Each Load()-instruction is "explicitly loading" the requested entities, so one database roundtrip per call.

Thus Include() will most probably be the more sensible choice in this case, but it depends on the database layout, how often this code is called and how long your DbContext lives. Why don't you try both ways and profile the queries and compare the timings?

See Loading Related Entities.