What could cause many data access exceptions using EF code first in a custom RoleProvider?

问题

My role provider looks like the class below (abridged). I am running on IIS Express, and SQL 2012 Express, from VS 2012, and I get a multitude of seemingly random exceptions in this role provider code.

public class Educ8RoleProvider : RoleProvider
{
    private readonly Educ8DbContext _dbContext = new Educ8DbContext();
    private readonly Authorization _authorization;
    public Educ8RoleProvider()
    {
        _authorization = new Authorization(_dbContext);
    }
    public override void Initialize(string name, System.Collections.Specialized.NameValueCollection config)
    {
        try
        {
            base.Initialize(name, config);
        }
        catch (Exception ex)
        {
            ErrorSignal.FromCurrentContext().Raise(ex);
            throw;
        }
    }
    public override bool IsUserInRole(string username, string roleName)
    {
        return GetRolesForUser(username).Any(r => r.ToLower() == roleName);
    }
    public override string[] GetRolesForUser(string username)
    {
        return _authorization.GetRolesForMember(username).Select(r => r.Name).ToArray();
    }
}

Here is a sample of my Authorization class:

public class Authorization
{
    private readonly Educ8DbContext _dbContext;
    private readonly IMemberRepository _memberRepository;
    private readonly IRoleRepository _roleRepository;
    private readonly IMemberRoleRepository _memberRoleRepository;
    public Authorization(Educ8DbContext context)
    {
        _dbContext = context;
        _memberRepository = new MemberRepository(_dbContext);
        _roleRepository = new RoleRepository(_dbContext);
        _memberRoleRepository = new MemberRoleRepository(_dbContext);
    }
    public IQueryable<Role> GetRoles()
    {
        return _roleRepository.ListAll();
    }
    public IQueryable<Role> GetRolesForMember(int memberId)
    {
        var roleIds = _memberRoleRepository.ListAll()
            .Where(mr => mr.MemberId == memberId)
            .Select(mr => mr.RoleId);
        return _roleRepository.ListAll()
            .Where(r => roleIds.Contains(r.Id));
    }
}

I get about two to three of the following exceptions every hour. Restarting the project immediately solves the problem, until the next one.

• Not allowed to change the 'ConnectionString' property. The connection's current state is closed.
• The context cannot be used while the model is being created.
• The underlying provider failed on Open.

It may be worth noting that I have absolutely zero data access issues anywhere else in the project.

Any suggestions on what may be causing this would be most welcome.

回答1:

Gert Arnold is on the right track with his comment. You have to realize that the RoleProvider runs as a singleton. Each time you restart your app, it is causing a new instance of this class to be constructed. As long as your application is running, it keeps using this one single instance.

I used to get the same kinds of exceptions as in your question before I realized that this class runs as a singleton. After you have that knowledge, it is not difficult to make these exceptions go away:

public class Educ8RoleProvider : RoleProvider
{
    //private readonly Educ8DbContext _dbContext = new Educ8DbContext();
    //private readonly Authorization _authorization;
    public Educ8RoleProvider()
    {
        //_authorization = new Authorization(_dbContext);
    }

    private Authorization GetAuthorization()
    {
        return new Authorization(new Educ8DbContext());
    }

    public override void Initialize(string name, NameValueCollection config)
    {
        try
        {
            base.Initialize(name, config);
        }
        catch (Exception ex)
        {
            ErrorSignal.FromCurrentContext().Raise(ex);
            throw;
        }
    }
    public override bool IsUserInRole(string username, string roleName)
    {
        return GetRolesForUser(username)
            .Any(r => r.ToLower() == roleName);
    }
    public override string[] GetRolesForUser(string username)
    {
        return GetAuthorization().GetRolesForMember(username)
            .Select(r => r.Name).ToArray();
    }
}

Essentially, you want to make sure that each method call on the RoleProvider works with a brand new DbContext instance. This way, the RoleProvider singleton is not hanging onto a single DbContext that gets stale.

来源：https://stackoverflow.com/questions/12677975/what-could-cause-many-data-access-exceptions-using-ef-code-first-in-a-custom-rol