Question 87692 in ASP.NET Question posted in
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LINQ To Entity – Inner Join issue – Asp.net

I have two related tables like below :

Users :

public partial class Users
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
    public Users()
    {

    }

    public int ID { get; set; }
    public int UserType_ID { get; set; }
    public string Email { get; set; }

    public virtual UserTypes UserTypes { get; set; }
}

UserTypes :

public partial class UserTypes
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
    public UserTypes()
    {
        this.Users = new HashSet<Users>();
    }

    public int ID { get; set; }
    public string Name { get; set; }
    public string Title { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<Users> Users { get; set; }
}

For access Name of UserType i wrote this linq to entity :

string[] UserTypes = new string[1];

using (Crypto_Entities entities = new Crypto_Entities())
{
    int User_ID_Integer = int.Parse(User_ID.Trim());

    var user = (from User in entities.Users
                //join UserType in entities.UserTypes on User.UserType_ID equals UserType.ID
                where User.ID == User_ID_Integer
                select User).FirstOrDefault();
    if (user != null)
    {
        UserTypes[0] = user.UserTypes.Name;
    }
}

My question is why user.Name does not work for my purpose and what is the benefit of join in linq to entity?
If i remove join as i did in my query i still can see Name field of UserType with user.UserTypes.Name.

Tags:

2

Answers


  1. 0

    Since you have set up the relations in your entities you don’t need to manually write join to load related data:

    var user = entities.Users
   .Include(u => u.UserTypes)
   .Where(u => u.ID == User_ID_Integer)
   .FirstOrDefault();

    As for your join being useless – EF Core translates the code into actual SQL (which you can check) and since you are not selecting any data from the joined table – it is as useless as it would be in SQL query where you have selected fields only from one table of join result.

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  2. 0

    You do not need join if you have defined correctly navigation properties. And if you just need Name, do not retrieve full entity.

    string[] UserTypes = new string[1];

using (Crypto_Entities entities = new Crypto_Entities())
{
    int User_ID_Integer = int.Parse(User_ID.Trim());

    var query = 
        from User in entities.Users
        where User.ID == User_ID_Integer
        select User.UserTypes.Name;

    var name = query.FirstOrDefault();
    if (name != null)
    {
        UserTypes[0] = name;
    }
}

    If you use navigation property in query, EF automatically generates all needed joins. But if you just select whole entity without defining Include – EF will not load related data. It makes sense, because otherwise you may load almost whole database if there are a lot of relations.

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