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Lazy loading in a detailed manner – Entity Framework

31 Dec

By default EF has lazy loading behavior. Due to this default behavior if you are loading a large number of records and especially if they have foreign key relationships, you can have performance issues. So you need to be cautious if you really need lazy loading behavior for all scenarios. For better performance, disable lazy loading when you are loading a large number of records or use stored procedures.

Lazy loading is a concept where we load objects on demand rather than loading everything in one go. Consider a situation where you have 1 to many relationships between the Customer and Address objects. Now let’s say you are browsing the customer data but you do not want address data to be loaded at that moment. But the time you start accessing the address object you would like to load address data from the database.

Entity Framework has lazy loading behavior by default enabled. For instance, consider the below code. When we are doing a foreach on the Customer object, the Address object is not loaded. But the time you start doing foreach on the address collection, the Address object is loaded from SQL Server by firing SQL queries.

So in simple words, it will fire a separate query for each address record of the customer, which is definitely not good for a large number of records.

MyEntities context = new MyEntities();

var Customers = context.Customers.ToList();

foreach (Customercust in Customers) // In this line no address object loaded
{
     foreach(Address add in cust.Addresses){} // Address object is loaded here
}
 

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