小编abd*_*dru的帖子

我有以下select组件,它来自rest api的数据.如何在md-select上设置默认选择值？

  <md-select
                placeholder= "Warehouse"
                style="width: 100%"
                [(ngModel)]='selectedProductWarehouse.warehouse'
                name="Warehouse"
                required
                #Warehouse="ngModel">
          <md-option *ngFor="let warehouse of warehouses" [value]="warehouse">{{warehouse.description}}</md-option>
        </md-select>

当我尝试从 asp.net web api 插入用户时出现以下异常： Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while updating the entries. See the inner exception for details. ---> Npgsql.PostgresException: 23505: duplicate key value violates unique constraint

以下是我的实体模型：角色和用户。其中每个用户都链接到一个角色。

public class Role
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public DateTime DateCreated { get; set; }
    public DateTime? LastUpdate { get; set; }
}

public class User
{
    public int Id { get; set; } …