{
  'detail[0].title':['message'],
  'detail[0].detail[0].title':['message']
}

  private findFieldControl(fieldName: string): AbstractControl {
    const path = fieldName.replace('[', '.').replace(']', '');
    return (
      this.form.get(path) || this.form.get(this.lowerCaseFirstLetter(path))
    );
  }

'detail.0.title'
'detail.0.detail.0.title'

protected handleSubmitError(response: HttpErrorResponse) {
    this.messages = [];

    if (response.status === 400) {
      // handle validation errors
      const validationDictionary = response.error;
      for (const fieldName in validationDictionary) {
        if (validationDictionary.hasOwnProperty(fieldName)) {
          const messages = validationDictionary[fieldName];
          const control = this.findFieldControl(fieldName);
          if (control) {
            // integrate into angular's validation if we have field validation
            control.setErrors({
              model: { messages: messages }
            });
          } else {
            // if we have cross field validation, then show the validation error at the top of the screen
            this.messages.push(...messages);
          }
        }
      }
    } else {
      this.messages.push('something went wrong!');
    }
  }

this.form = this.formBuilder.group({
      userName: [
        '',
        [Validators.required, UserNameValidators.rule1)]
      ],
      password: ['', Validators.required],
      rememberMe: [false]
    });

export class UserNameValidators{
   static rule1(control: AbstractControl) {
        if (control.value.indexOf(' ') >= 0) {
            return { rule1: true };
        }
        return null;
    }
}

 public class AuthorizationPolicyProvider : DefaultAuthorizationPolicyProvider
    {
        private readonly LazyConcurrentDictionary<string, AuthorizationPolicy> _policies =
            new LazyConcurrentDictionary<string, AuthorizationPolicy>();

        public AuthorizationPolicyProvider(IOptions<AuthorizationOptions> options)
            : base(options)
        {
        }

        public override async Task<AuthorizationPolicy> GetPolicyAsync(string policyName)
        {
           //...
        }
    }

        public override async Task<AuthorizationPolicy> GetPolicyAsync(string policyName)
        {
          //...

            var policy = _policies.GetOrAdd(policyName, name =>
            {
                var permissionNames = policyName.Substring(PermissionAuthorizeAttribute.PolicyPrefix.Length).Split(',');

                return new AuthorizationPolicyBuilder()
                    .RequireClaim(CustomClaimTypes.Permission, permissionNames)
                    .Build();
            });

            return policy;
        }

var student = new Student() {
    StudentId = 50
};

using (var context = new SchoolContext()) {

    context.Remove<Student>(student);

    context.SaveChanges();
}

/// Example: "00001.00042.00005".

/// Example: "00001.00042.00006".

    public class OrganizationalUnit : TrackableEntity<User>, IHasRowVersion, IPassivable
    {
        #region Constants

        /// <summary>
        /// Maximum depth of an UO hierarchy.
        /// </summary>
        public const int MaxDepth = 16;

        /// <summary>
        /// Length of a code unit between dots.
        /// </summary>
        public const int PathUnitLength = 5;

        /// <summary>
        /// Maximum length of the <see cref="Path"/> property.
        /// </summary>
        public const int MaxPathLength = MaxDepth * (PathUnitLength + 1) - 1;

        public const char HierarchicalDisplayNameSeperator = '»';

        #endregion

        #region Properties

        public string Name { get; set; }
        public string NormalizedName { get; set; }
        public string HierarchicalDisplayName { get; set; }
        /// <summary>
        /// Hierarchical Path of this organization unit.
        /// Example: "00001.00042.00005".
        /// It's changeable if OU hierarch is changed.
        /// </summary>
        public string Path { get; set; }
        public bool IsActive { get; set; } = true;
        public byte[] RowVersion { get; set; }

        #endregion

        #region Navigation Properties

        public OrganizationalUnit Parent { get; set; }
        public long? ParentId { get; set; }
        public ICollection<OrganizationalUnit> Children { get; set; } = new HashSet<OrganizationalUnit>();
        public ICollection<UserOrganizationalUnit> UserOrganizationalUnits { get; set; } =
            new HashSet<UserOrganizationalUnit>();

        #endregion

        #region Public Methods

        /// <summary>
        /// Creates path for given numbers.
        /// Example: if numbers are 4,2 then returns "00004.00002";
        /// </summary>
        /// <param name="numbers">Numbers</param>
        public static string CreatePath(params int[] numbers)
        {
            if (numbers.IsNullOrEmpty())
            {
                return null;
            }

            return numbers.Select(number => number.ToString(new string('0', PathUnitLength))).JoinAsString(".");
        }

        /// <summary>
        /// Appends a child path to a parent path. 
        /// Example: if parentPath = "00001", childPath = "00042" then returns "00001.00042".
        /// </summary>
        /// <param name="parentPath">Parent path. Can be null or empty if parent is a root.</param>
        /// <param name="childPath">Child path.</param>
        public static string AppendPath(string parentPath, string childPath)
        {
            if (childPath.IsNullOrEmpty())
            {
                throw new ArgumentNullException(nameof(childPath), "childPath can not be null or empty.");
            }

            if (parentPath.IsNullOrEmpty())
            {
                return childPath;
            }

            return parentPath + "." + childPath;
        }

        /// <summary>
        /// Gets relative path to the parent.
        /// Example: if path = "00019.00055.00001" and parentPath = "00019" then returns "00055.00001".
        /// </summary>
        /// <param name="path">The path.</param>
        /// <param name="parentPath">The parent path.</param>
        public static string GetRelativePath(string path, string parentPath)
        {
            if (path.IsNullOrEmpty())
            {
                throw new ArgumentNullException(nameof(path), "Path can not be null or empty.");
            }

            if (parentPath.IsNullOrEmpty())
            {
                return path;
            }

            if (path.Length == parentPath.Length)
            {
                return null;
            }

            return path.Substring(parentPath.Length + 1);
        }

        /// <summary>
        /// Calculates next path for given path.
        /// Example: if code = "00019.00055.00001" returns "00019.00055.00002".
        /// </summary>
        /// <param name="path">The path.</param>
        public static string CalculateNextPath(string path)
        {
            if (path.IsNullOrEmpty())
            {
                throw new ArgumentNullException(nameof(path), "Path can not be null or empty.");
            }

            var parentPath = GetParentPath(path);
            var lastUnitPath = GetLastUnitPath(path);

            return AppendPath(parentPath, CreatePath(Convert.ToInt32(lastUnitPath) + 1));
        }

        /// <summary>
        /// Gets the last unit path.
        /// Example: if path = "00019.00055.00001" returns "00001".
        /// </summary>
        /// <param name="path">The path.</param>
        public static string GetLastUnitPath(string path)
        {
            if (path.IsNullOrEmpty())
            {
                throw new ArgumentNullException(nameof(path), "Path can not be null or empty.");
            }

            var splittedPath = path.Split('.');
            return splittedPath[splittedPath.Length - 1];
        }

        /// <summary>
        /// Gets parent path.
        /// Example: if path = "00019.00055.00001" returns "00019.00055".
        /// </summary>
        /// <param name="path">The path.</param>
        public static string GetParentPath(string path)
        {
            if (path.IsNullOrEmpty())
            {
                throw new ArgumentNullException(nameof(path), "Path can not be null or empty.");
            }

            var splittedPath = path.Split('.');
            if (splittedPath.Length == 1)
            {
                return null;
            }

            return splittedPath.Take(splittedPath.Length - 1).JoinAsString(".");
        }

        #endregion
    }

       public virtual async Task<string> GetNextChildPathAsync(long? parentId)
        {
            var lastChild = await GetLastChildOrNullAsync(parentId).ConfigureAwait(false);
            if (lastChild == null)
            {
                var parentPath = parentId != null ? await GetPathAsync(parentId.Value).ConfigureAwait(false) : null;
                return OrganizationalUnit.AppendPath(parentPath, OrganizationalUnit.CreatePath(1));
            }

            return OrganizationalUnit.CalculateNextPath(lastChild.Path);
        }

        public async Task<string> GetNextChildHierarchicalDisplayNameAsync(string name, long? parentId)
        {
            var parent = parentId != null
                ? await _organizationalUnits.SingleOrDefaultAsync(a => a.Id == parentId.Value).ConfigureAwait(false)
                : null;

            return parent == null
                ? name
                : $"{parent.HierarchicalDisplayName} {OrganizationalUnit.HierarchicalDisplayNameSeperator} {name}";
        }

        public virtual async Task<OrganizationalUnit> GetLastChildOrNullAsync(long? parentId)
        {
            return await _organizationalUnits.OrderByDescending(c => c.Path)
                .FirstOrDefaultAsync(ou => ou.ParentId == parentId).ConfigureAwait(false);
        }

        public virtual async Task<string> GetPathAsync(long id)
        {
            Guard.ArgumentNotZero(id, nameof(id));
            var organizationalUnit = await _organizationalUnits.SingleOrDefaultAsync(ou => ou.Id == id).ConfigureAwait(false);
            if (organizationalUnit == null)
            {
                throw new KeyNotFoundException();
            }
            return organizationalUnit.Path;
        }

        public async Task<List<OrganizationalUnit>> FindChildrenAsync(long? parentId, bool recursive = false)
        {
            if (!recursive)
            {
                return await _organizationalUnits.Where(ou => ou.ParentId == parentId).ToListAsync().ConfigureAwait(false);
            }

            if (!parentId.HasValue)
            {
                return await _organizationalUnits.ToListAsync().ConfigureAwait(false);
            }

            var path = await GetPathAsync(parentId.Value).ConfigureAwait(false);

            return await _organizationalUnits.Where(
                ou => ou.Path.StartsWith(path) && ou.Id != parentId.Value).ToListAsync().ConfigureAwait(false);
        }

        public virtual async Task MoveAsync(long id, long? parentId)
        {
            Guard.ArgumentNotZero(id, nameof(id));
            var organizationalUnit = await _organizationalUnits.SingleOrDefaultAsync(ou => ou.Id == id).ConfigureAwait(false);
            if (organizationalUnit == null || organizationalUnit.ParentId == parentId)
            {
                return;
            }

            //Should find children before Path change
            var children = await FindChildrenAsync(id, true).ConfigureAwait(false);

            //Store old Path of OU
            var oldPath = organizationalUnit.Path;

            //Move OU
            organizationalUnit.Path = await GetNextChildPathAsync(parentId).ConfigureAwait(false);
            organizationalUnit.ParentId = parentId;

            //Update Children Paths
            foreach (var child in children)
            {
                child.Path = OrganizationalUnit.AppendPath(organizationalUnit.Path, OrganizationalUnit.GetRelativePath(child.Path, oldPath));
            }
        }