CODEWITHSUNDEEP
asp.netasp.net-mvc
user2583498
user2583498

Reputation:

Null Exception on a Nullable<int>

I have the following model class inside my asp.net mvc web application:

public class SecurityRoleGroupAssign
{
    public  IEnumerable<TechnologyType> TechnologyType {get; set;}
    public  IEnumerable<PermisionLevel> PermisionLevel {get; set;}
    public SecurityRole SecurityRole { get; set; }
    public Nullable<int> rackPermisionLevel { get; set; }
    public Nullable<int> serverPermisionLevel { get; set; }
    public Nullable<int> routerPermisionLevel { get; set; }
    public Nullable<int> virtualMachinePermisionLevel { get; set; }
    public Nullable<int>  switchPermisionLevel { get; set; }
}

But when I tried to populate this class I got a Null Exception:-

public SecurityRoleGroupAssign populateSecurityRolePermisionLevelAssign(int RoleID)
{
    SecurityRoleGroupAssign c = new SecurityRoleGroupAssign
    {
        SecurityRole = FindAllRole(RoleID),
        PermisionLevel = tms.PermisionLevels.ToList(),
        TechnologyType = tms.TechnologyTypes.ToList(),
        serverPermisionLevel = tms.SecurityroleTypePermisions
         .Where(a=>a.SecurityRoleID == RoleID)
         .Where(a2=>a2.TechnologyType.Name.ToLower() == "server")
         .SingleOrDefault().PermisionLevelID,
        rackPermisionLevel = tms.SecurityroleTypePermisions
         .Where(a => a.SecurityRoleID == RoleID)
         .Where(a2 => a2.TechnologyType.Name.ToLower() == "rack")
         .SingleOrDefault().PermisionLevelID,
        virtualMachinePermisionLevel = tms.SecurityroleTypePermisions
         .Where(a=>a.SecurityRoleID == RoleID)
         .Where(a2=>a2.TechnologyType.Name.ToLower() == "virtual machine")
         .SingleOrDefault().PermisionLevelID,
        routerPermisionLevel = tms.SecurityroleTypePermisions
         .Where(a=>a.SecurityRoleID == RoleID)
         .Where(a2=>a2.TechnologyType.Name.ToLower() == "router")
         .SingleOrDefault().PermisionLevelID,
        switchPermisionLevel = tms.SecurityroleTypePermisions
         .Where(a => a.SecurityRoleID == RoleID)
         .Where(a2 => a2.TechnologyType.Name.ToLower() == "switch")
         .SingleOrDefault().PermisionLevelID
    };
    return c;
}

Upvotes: 0

Views: 112

Answers (2)

p.s.w.g
p.s.w.g

Reputation: 148980

The problem is that SingleOrDefault will return null (for reference types) if no items exist. So any time you call .SingleOrDefault().PermisionLevelID you're in danger of a null reference exception. you can fix this by placing the .SingleOrDefault() after the selected the result—e.g.(... select p.PermissionLevelID).SingleOrDefault().

Try this:

var permissions = tms.SecurityroleTypePermisions.Where(a => a.SecurityRoleID == RoleID);
SecurityRoleGroupAssign c = new SecurityRoleGroupAssign
{
    SecurityRole = FindAllRole(RoleID),
    PermisionLevel = tms.PermisionLevels.ToList(),
    TechnologyType = tms.TechnologyTypes.ToList(),
    serverPermisionLevel = 
        (from p in permissions
         where p.TechnologyType.Name.ToLower() == "server"
         select p.PermisionLevelID)
        .SingleOrDefault(),
    rackPermisionLevel = 
        (from p in permissions
         where p.TechnologyType.Name.ToLower() == "rack"
         select p.PermisionLevelID)
        .SingleOrDefault(),
    virtualMachinePermisionLevel = 
        (from p in permissions
         where p.TechnologyType.Name.ToLower() == "virtual" 
         select p.PermisionLevelID)
        .SingleOrDefault(),
    routerPermisionLevel = 
        (from p in permissions
         where p.TechnologyType.Name.ToLower() == "router")
         select p.PermisionLevelID
        .SingleOrDefault(),
    switchPermisionLevel =
        (from p in permissions
         where p.TechnologyType.Name.ToLower() == "switch"
         select p.PermisionLevelID
        .SingleOrDefault()
};

Or better yet:

var permissions = tms.SecurityroleTypePermisions
                     .Where(a => a.SecurityRoleID == RoleID)
                     .ToLookup(a => a.TechnologyType.Name.ToLower(),
                               a => a.PermisionLevelID);
SecurityRoleGroupAssign c = new SecurityRoleGroupAssign
{
    SecurityRole = FindAllRole(RoleID),
    PermisionLevel = tms.PermisionLevels.ToList(),
    TechnologyType = tms.TechnologyTypes.ToList(),
    serverPermisionLevel = permissions["server"].SingleOrDefault(),
    rackPermisionLevel = permissions["rack"].SingleOrDefault(),
    virtualMachinePermisionLevel = permissions["virtual"].SingleOrDefault(),
    routerPermisionLevel = permissions["router"].SingleOrDefault(),
    switchPermisionLevel = permissions["switch"].SingleOrDefault()
};

Upvotes: 2

Thousand
Thousand

Reputation: 6638

.SingleOrDefault():

Returns the only element of a sequence, or a default value if the sequence is empty; this method throws an exception if there is more than one element in the sequence.

serverPermisionLevel = tms.SecurityroleTypePermisions.Where(a=>a.SecurityRoleID == RoleID).Where(a2=>a2.TechnologyType.Name.ToLower() == "server").SingleOrDefault().PermisionLevelID;

The problem here is that the .SingleOrDefault(); call returned the default "null" value. The error is thrown when you try to call the PermissionLevelID on that null reference.

What you could change it into:

 serverPermisionLevel = tms.SecurityroleTypePermisions
.Where(a=>a.SecurityRoleID == RoleID)
.Where(a2=>a2.TechnologyType.Name.ToLower() == "server")
.Select(r => r.PermissionLevelID).SingleOrDefault();

this way, your nullable ints will be filled when .SingleOrDefault actually returns null, or with the actual value of the PermissionLevelId if there is one.

Upvotes: 1

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