Can Entity Framework's `Include()` Method Handle Multiple Levels of Nested Properties?

Entity Framework multi-level attribute loading

Entity Framework's Include() method can efficiently preload related entities, but can it handle multiple levels of nested properties (such as nested collections containing complex objects)?

Existing implementation and limitations

The sample code shows that the Include() method can load first-level properties. Query as follows:

<code class="language-csharp">public IEnumerable<applicationserver> GetAll()
{
    return this.Database.ApplicationServers
        .Include(x => x.ApplicationsWithOverrideGroup)
        .Include(x => x.ApplicationWithGroupToForceInstallList)
        .Include(x => x.CustomVariableGroups)
        .ToList();
}</code>

will retrieve a ApplicationsWithOverrideGroup object containing a ApplicationServer property, which contains a collection of ApplicationWithOverrideVariableGroup objects. However, the ApplicationWithOverrideVariableGroup and Application properties in the CustomVariableGroup collection will not be populated.

Solution for multi-level nested Include

Depending on the version of Entity Framework used, multi-level properties can be preloaded using the following methods:

Entity Framework 6:

Entity Framework 6’s Include() method accepts a lambda expression. By using nested lambda expressions, you can specify multiple levels of inclusion:

<code class="language-csharp">var query = this.Database.ApplicationServers
    .Include(x => x.ApplicationsWithOverrideGroup
        .Select(y => y.Application))
    .Include(x => x.ApplicationsWithOverrideGroup
        .Select(y => y.CustomVariableGroup));</code>

Entity Framework Core:

Entity Framework Core introduces the ThenInclude() method, allowing cascading includes. This method is used after the initial Include() to specify deeper inclusion:

<code class="language-csharp">var query = this.Database.ApplicationServers
    .Include(x => x.ApplicationsWithOverrideGroup)
    .ThenInclude(y => y.Application)
    .ThenInclude(y => y.CustomVariableGroup);</code>

Through these methods, you can preload multi-level properties in Entity Framework, ensuring that complex object collections are fully populated upon retrieval.

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