- \n
- EF performs slower when it has to populate an Entity with deep hierarchy. Be extremely careful with entities with deep hierarchy<\/li>\n
- Indexing of database is good but in case of EF it becomes very important. The columns use for retrieval and sorting should be properly indexed.<\/li>\n
- When the model is large, VS2010\/VS2012 Model designer gets real crazy. so break the model into medium sized models. There is a limitation that the Entities from different models cannot be shared even though they may be pointing to the same table in the database.<\/li>\n
- Transactions are slow. be careful with them<\/li>\n<\/ul>\n
4) <\/strong>Why should not use Entity Framework or an ORM?<\/b><\/p>\n
- \n
- Bulk updates (in addition to bulk inserts)<\/li>\n
- Querying across multiple databases: EF currently restricts the entities in a single context to a single database. If you are forced to work with a multi-database setup, this could be an issue.<\/li>\n
- Lack of support for nullable keys: if you are dealing with a legacy data model where some tables have unique clustered indices with nullable columns, you will find EF unable to deal with this<\/li>\n<\/ul>\n
5)What is the importance of EDMX file in Entity Framework?<\/strong><\/p>\n
![\"Untitled\"](\"http:\/\/mairwa.com\/wordpress\/wp-content\/uploads\/2014\/08\/Untitled-300x58.gif\")
<\/a><\/b><\/p>\n<\/p>\n
EDMX (Entity Data Model XML) is an XML file which contains all the mapping details of how the objects map with SQL tables. The EDMX file is further divided into three sections: CSDL, SSDL, and MSL.<\/p>\n
6)Explain CSDL, SSDL and MSL sections in an EDMX file?<\/strong><\/p>\n
- \n
- CSDL (Conceptual Schema definition language) is the conceptual abstraction which is exposed to the application.<\/li>\n
- SSDL (Storage Schema Definition Language) defines the mapping with your RDBMS data structure.<\/li>\n
- MSL (Mapping Schema Language) connects the CSDL and SSDL.<\/li>\n<\/ul>\n
CSDL, SSDL and MSL are actually XML files.<\/p>\n
![\"Untitled\"](\"http:\/\/mairwa.com\/wordpress\/wp-content\/uploads\/2014\/08\/Untitled2.png\")
<\/a><\/p>\n<\/p>\n
7) What are T4 templates?<\/strong><\/p>\n
<\/p>\n
T4 (Text Template Transformation Toolkit) is a template based code generation engine. To \u00a0write C# code in T4 templates (.tt<\/em> is the extension) files and those C# codes execute to generate the file as per the written C# logic.<\/p>\n
For instance, the below T4 C# code:<\/p>\n
<#@ template language=”\u201cC#\u201d” #><\/p>\n
Hello <# Write(\u201dWorld!\u201d) #><\/p>\n
Will generate the following C# output:<\/p>\n
Hello<\/p>\n
World !<\/p>\n
Importance Of T4<\/b><\/p>\n
\u00a0 <\/b>It is EF code generation. The t4 code templates read the Edmx file and generate c# code behind. The c# code<\/p>\n
![\"Untitled\"](\"http:\/\/mairwa.com\/wordpress\/wp-content\/uploads\/2014\/08\/Untitled3.png\")
<\/a><\/p>\n8)How to read records using Entity framework?<\/strong><\/p>\n
We create the object of context class and inside this context class will get the records.<\/p>\n
Ex\u2014customercontext custe=new customercontext();<\/p>\n
Foreach(cusromer objcust in custe.customers){}<\/p>\n
9)People say Entity Framework runs slow<\/p>\n
By default EF has lazy loading behavior. Due to this default behavior if we are loading a large number of records and especially if they have foreign key relationships, we can have performance issues. So we need to be cautious if really need lazy loading behavior for all scenarios. For better performance, disable lazy loading when we are loading a large number of records or use stored procedures.<\/p>\n
<\/p>\n
10)Can you explain lazy loading in a detailed manner?<\/b><\/p>\n
Lazy loading is a concept where we load objects on demand rather than loading everything in one go. Consider a situation where we have 1 to many relationships between the Customer and Address objects. Now let\u2019s say we are browsing the customer data but we do not want address data to be loaded at that moment. But the time we start accessing the address object we would like to load address data from the database.<\/p>\n
Entity Framework has lazy loading behavior by default enabled. For instance, consider the below code. When we are doing a
foreach<\/code> on the Customer object, the Address object is not loaded. But the time we start doingforeach<\/code> on the address collection, the Address object is loaded from SQL Server by firing SQL queries.<\/p>\nSo 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.<\/p>\n
MyEntities context = new MyEntities();<\/sup><\/p>\n
\u00a0<\/sup><\/p>\n
var<\/sup> Customers = context.Customers.ToList();<\/sup><\/p>\n
\u00a0<\/sup><\/p>\n
foreach<\/sup> (Customercust in Customers) \/\/ In this line no address object loaded<\/sup><\/p>\n
{<\/sup><\/p>\n
\u00a0\u00a0\u00a0\u00a0 foreach(Address add in cust.Addresses){}\/\/ Address object is loaded here<\/sup><\/p>\n
}<\/sup><\/p>\n
\u00a0<\/sup><\/p>\n
11)How can we turn off lazy loading?<\/b><\/p>\n
The opposite of lazy loading is eager loading. In eager loading we load the objects beforehand. So the first thing is we need to disable lazy loading by setting
LazyLoadingEnabled<\/code> tofalse<\/code>.<\/p>\n- \n
- context.ContextOptions.LazyLoadingEnabled = false;<\/li>\n<\/ul>\n
Now we have to explicitly tell EF what objects we want to load by using the
include<\/code> function. Below is a simple sample code where we tell EF to load customer as well as address objects by using theinclude<\/code> function.<\/p>\nNow the customer object and the related address objects will be loaded in one query rather than multiple queries.<\/p>\n
- \n
- var employees = context.Customers.Include(“Addresses”).Take(5);<\/li>\n<\/ul>\n
12)What are POCO classes in Entity Framework?<\/b><\/p>\n
POCO means Plain Old C# Object. When EDMX creates classes, they are cluttered with a lot of entity tags. For instance, below is a simple customer class generated using Entity Framework. Many times we would like to use simple .NET classes and integrate them with Entity Framework.<\/p>\n
Entity Framework allows this. In other words you can create a simple .NET class and use the entity context object to load your simple .NET classes.<\/p>\n
Below is a simple class generated by EF which is cluttered with a lot of EF attributes.<\/p>\n
[EdmEntityTypeAttribute(NamespaceName=”CustomermytestModel”, Name=”Customer”)]<\/p>\n
[Serializable()]<\/p>\n
[DataContractAttribute(IsReference=true)]<\/p>\n
public partial class Customer : EntityObject<\/p>\n
{<\/p>\n
#region Factory Method<\/p>\n
<\/p>\n
\/\/\/ <summary><\/i><\/p>\n
\/\/\/ Create a new Customer object.<\/p>\n
\/\/\/ <\/summary><\/i><\/p>\n
\/\/\/ <param<\/i> name=”id”<\/i> \/><\/i>Initial value of the Id property.<\/p>\n
\/\/\/ <param<\/i> name=”customerCode”<\/i> \/><\/i>Initial value of the CustomerCode property.<\/p>\n
\/\/\/ <param<\/i> name=”customername”<\/i> \/><\/i>Initial value of the Customername property.<\/p>\n
public static Customer CreateCustomer(global::System.Int32 id,<\/p>\n
global::System.String customerCode, global::System.String customername)<\/p>\n
{<\/p>\n
Customer customer = new Customer();<\/p>\n
customer.Id = id;<\/p>\n
customer.CustomerCode = customerCode;<\/p>\n
customer.Customername = customername;<\/p>\n
return customer;<\/p>\n
}<\/p>\n
<\/p>\n
#endregion<\/p>\n
#region Primitive Properties<\/p>\n
13)How do we implement POCO in Entity Framework?<\/b><\/p>\n
To implement POCO is a three step process:<\/p>\n
Go to the designer and set the code generation strategy to
NONE<\/code>. This step means that we would be generating the classes on own rather than relying on EF auto code generation.<\/p>\nNow that we have stopped the auto generation of code, we need to create the domain classes manually. Add a class file and create the domain classes like the
Customer<\/code> class we created.<\/p>\npublic class Customer<\/p>\n
{<\/p>\n
private string _customerName;<\/p>\n
<\/p>\n
public string CustomerName<\/p>\n
{<\/p>\n
get { return _customerName; }<\/p>\n
set { _customerName = value; }<\/p>\n
}<\/p>\n
<\/p>\n
private int _Customerid;<\/p>\n
<\/p>\n
public int Customerid<\/p>\n
{<\/p>\n
get { return _Customerid; }<\/p>\n
set { _Customerid = value; }<\/p>\n
}<\/p>\n
<\/p>\n
}<\/p>\n
- \n
- Write your Context layer code inheriting from
ObjectContext<\/code>. Disable auto-generation.<\/li>\n<\/ul>\npublic partial class Test123Entities : ObjectContext<\/p>\n
{<\/p>\n
public Test123Entities()<\/p>\n
: base(“name=Test123Entities”, “Test123Entities”)<\/p>\n
{<\/p>\n
this.ContextOptions.LazyLoadingEnabled = true;<\/p>\n
OnContextCreated();<\/p>\n
}<\/p>\n
partial void OnContextCreated();<\/p>\n
public ObjectSet<Customer> Customers<\/p>\n
{<\/p>\n
get<\/p>\n
{<\/p>\n
if ((_Customers == null))<\/p>\n
{<\/p>\n
_Customers = base.CreateObjectSet<Customer>(“Customers”);<\/p>\n
}<\/p>\n
return _Customers;<\/p>\n
}<\/p>\n
}<\/p>\n
private ObjectSet<Customer> _Customers;<\/p>\n
public void AddToCustomers(Customer customer)<\/p>\n
{<\/p>\n
base.AddObject(“Customers”, customer);<\/p>\n
}<\/p>\n
}<\/p>\n
And finally we can use the above code in client as if where using EF normally.<\/p>\n
Test123Entities oContext = new Test123Entities();<\/p>\n
List<Customer> oCustomers = oContext.Customers.ToList<Customer>();<\/p>\n
14)In POCO classes do we need EDMX files?<\/b><\/p>\n
Yes, still need EDMX files because the context object reads the EDMX files to do the mapping.<\/p>\n
15)What is Code First approach in Entity Framework?<\/b><\/p>\n
In Code First approach we avoid working with the Visual Designer of Entity Framework. In other words the EDMX file is excluded from the solution. So now have complete control over the context class as well as the entity classes.<\/p>\n
16)What is the difference between POCO, Code First, and simple EF approach?<\/b><\/p>\n
All these three approaches define how much control you want on your Entity Framework code. Entity Framework is an OR mapper, it generates a lot of code, it creates middle tier (Entity), and Data Access layer (Context).<\/p>\n
But a lot of times we want to enjoy the benefits of both worlds, we want the auto-generation part to minimize development time and also want control on the code so that we can maintain code quality.<\/p>\n
Below is the difference table which defines each of the approaches. In simple Entity Framework, everything is auto generated and so we need the EDMX XML file as well. POCO is semi-automatic so we have full control on the entity classes but then the context classes are still generated by the EDMX file.<\/p>\n
In Code First, you have complete control on how you can create the entity and context classes. Because you are going to manually create these classes, you do not have dependency on the EDMX XML file. Below is a simple table which shows the cross comparison.<\/p>\n
- Write your Context layer code inheriting from
- var employees = context.Customers.Include(“Addresses”).Take(5);<\/li>\n<\/ul>\n
- context.ContextOptions.LazyLoadingEnabled = false;<\/li>\n<\/ul>\n
![\"Untitled\"](\"http:\/\/mairwa.com\/wordpress\/wp-content\/uploads\/2014\/08\/Untitled.gif\")
<\/a><\/b><\/p>\n![\u00a0<\/a>30)Difference between ObjectContext and DbContext<\/strong><\/p>\nObjectContext<\/b><\/p>\nObjectContext is a class that manages all the database operations, like database connection, and manages various entities of the Entity Model. We can say that ObjectContext is the primary class for accessing or working together with entities that are defined in the conceptual model.<\/p>\n <\/p>\nDbContext\n<\/b>\nDbContext is conceptually similar to ObjectContext. DbContext is nothing but a ObjectContext wrapper, we can say it is a lightweight alternative to the ObjectContext. DbContext can be used for DataBase first, code first and model first development. DbContext mainly contains a set of APIs that\u00a0are very easy to use. The API is exposed by ObjectContext. These APIs also allow us to use a Code First approach that ObjectContext does not allow.<\/p>\n <\/p>\nObjectContext VS DbContext<\/b><\/p>\n\n\n\nObjectContext<\/b><\/td>\nDbContext<\/b><\/td>\n<\/tr>\n\nObjectContext class is part of the core Entity Framework API, that allows us to perform queries, change and track updates of the Database by using strongly typed entity classes.<\/td>\nThe DbContext class can be described as a wrapper of ObjectContext. It exposes the most commonly used features of ObjectContext.<\/td>\n<\/tr>\n\nObjectContext supports Compiled Queries.<\/td>\nDbContext does not support Compiled Queries.<\/td>\n<\/tr>\n\nObjectContext supports self-tracking of Entities<\/td>\nDbContext does not support self-tracking of Entities.<\/td>\n<\/tr>\n\nObjectContext is only useful in Model First and Database First approaches<\/td>\nDbContext is useful in Model First, Database First approach as well as Code First approach.<\/td>\n<\/tr>\n\nObjectContext can be used by Entity Framework 4.0 and below.<\/td>\nDBContext can be used by Entity Framework 4.1 and above.<\/td>\n<\/tr>\n\nThe ObjectContext class is not thread-safe.<\/td>\nAny public static (C#) or Shared (Visual Basic) members of DbContext are thread-safe. Any instance members are not guaranteed to be thread safe.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nThere are also many methods in common in both ObjectContext and DbContext. For example ObjectContext has a direct method to execute\u00a0a query against a database whereas the DbContext.DataBase class contains the SQLQuery method to\u00a0obtain the same result.<\/p>\nExample<\/b><\/p>\n\/\/ using ObjectContext (EF4.0)\nusing\u00a0(Entities\u00a0context =\u00a0new\u00a0Entities())\n{\nIEnumerable<EmployeeDetails> empDetails \u00a0= \u00a0context.ExecuteStoreQuery<EmployeeDetails>\n(“exec GetEmployeeData”).ToList();\n}<\/p>\n\/\/ using DBContext (EF 4.1 and above)\nusing\u00a0(Entities\u00a0context =\u00a0new\u00a0Entities())\n{\nIEnumerable<EmployeeDetails> empDetails \u00a0= \u00a0context. Database.SqlQuery\n<\u00a0EmployeeDetails\u00a0>(“exec\u00a0GetEmployeeData\u00a0“, null).ToList();\n}<\/p>\nDbContext also has some sets of methods that are not available with ObjectContext, like Dbset.Find, DbSet.Local etcetera.<\/p>\nSome of the ObjectContext methods are also renamed. For example ObjectContext has methods like AddObject, DeleteObject And Attech on ObjectSet<T>, in DbContext, they are named Add, Remove and Attach on DbSet<TEntity>.<\/p>\n","protected":false},"excerpt":{"rendered":"1) What is the advantage and disadvantage of Entity Framework Advantages: One common syntax (LINQ) for all object queries whether it is database or not , Pretty fast if used as intended , easy to implement SoC , less coding required to accomplish complex tasks. Its fast and straight forward using LINQ\/FE objects For Add\/Modify\/Delete\/Update. Easy to map business objects… Read more →<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[],"class_list":["post-95","post","type-post","status-publish","format-standard","hentry","category-ado-net-entity-framework","xfolkentry"],"_links":{"self":[{"href":"http:\/\/mairwa.com\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/95","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/mairwa.com\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/mairwa.com\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/mairwa.com\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/mairwa.com\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=95"}],"version-history":[{"count":0,"href":"http:\/\/mairwa.com\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/95\/revisions"}],"wp:attachment":[{"href":"http:\/\/mairwa.com\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=95"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/mairwa.com\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=95"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/mairwa.com\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=95"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}](\"http:\/\/mairwa.com\/wordpress\/wp-content\/uploads\/2014\/08\/Untitled4.png\"){kind=link}