无法转换类型为“System.Data.Entity.Infrastructure.DbQuery”的对象

Question

当我尝试按字段名称 uuid 查找记录时，出现以下错误：

{"无法将类型为 'System.Data.Entity.Infrastructure.DbQuery`1[SyncBank.Models.XeroBankAccount]' 的对象转换为类型 'SyncBank.Models.XeroBankAccount'

public XeroBankAccount FindAccountByUuid(String uuid)
        {
            try
            {
                using (SyncBankDbContext dbContext = new SyncBankDbContext())
                {
                    string tempUuid = uuid;
                    var result = (XeroBankAccount) dbContext.XeroBankAccounts.Where(x => x.AccountUuid == tempUuid);
                    return result;
                }
            }
            catch (Exception e)
            {
                string errorMessage = e.Message;
                return null;
            }
        }

错误：

{"Unable to cast object of type 'System.Data.Entity.Infrastructure.DbQuery`1[SyncBank.Models.XeroBankAccount]' to type 'SyncBank.Models.XeroBankAccount'."}

XeroBankAccount.cs：

using System;
using System.ComponentModel.DataAnnotations.Schema;
using System.ComponentModel.DataAnnotations;
using SyncBank.Xero;

namespace SyncBank.Models
{
    [Serializable]
    [Table("xero_bank_account")]
    public class XeroBankAccount
    {

        [Key]
        [Column("id")]
        public int Id { get; set; }

        [ForeignKey("XeroOrganisation")]
        [Column("organisation_id")]
        public int XeroOrganisationId { get; set; }

        public XeroOrganisation XeroOrganisation { get; set; }

        [Column("bank_id")]
        public int? BankId { get; set; }


        [Column("title")]
        [MinLength(1), MaxLength(128)]
        [Required]
        public String AccountTitle { get; set; }

        [Column("number")]
        [StringLength(50)]
        public String AccountNumber { get; set; }

        [Column("balance_statement")]
        public double? BalanceStatement { get; set; }

        [Column("balance_xero")]
        public double? BalanceXero { get; set; }

        [Column("last_statement_date")]
        public DateTime? LastStatementDate { get; set; }

        [Column("reconciled")]
        public BankAccountReconciled? Reconciled { get; set; }

        [Required]
        [Column("uuid")]
        [StringLength(256)]
        public string AccountUuid { get; set; }

        [Column("orders")]
        public int Orders { get; set; }

        public override int GetHashCode()
        {
            return Id.GetHashCode();
        }

        public override bool Equals(Object obj)
        {
            // TODO: Warning - this method won't work in the case the id fields are not set
            if (!(obj is XeroBankAccount))
            {
                return false;
            }
            XeroBankAccount other = (XeroBankAccount)obj;
            return Id == other.Id;
        }

        public override String ToString()
        {
            return "org.syncbank.entity.XeroBankAccount[ accountId=" + Id + " ]";
        }
    }
}

SQL xero_bank_account：

CREATE TABLE `xero_bank_account` (
  `id` int(11) NOT NULL,
  `organisation_id` int(11) NOT NULL,
  `bank_id` int(11) DEFAULT NULL,
  `title` varchar(128) NOT NULL,
  `number` varchar(50) DEFAULT NULL,
  `balance_statement` decimal(12,2) DEFAULT NULL,
  `balance_xero` decimal(12,2) DEFAULT NULL,
  `reconciled` enum('true','false') NOT NULL DEFAULT 'false',
  `last_statement_date` datetime DEFAULT NULL,
  `uuid` varchar(256) CHARACTER SET latin1 COLLATE latin1_bin NOT NULL,
  `orders` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

--
-- Indexes for dumped tables
--

--
-- Indexes for table `xero_bank_account`
--
ALTER TABLE `xero_bank_account`
  ADD PRIMARY KEY (`id`),
  ADD UNIQUE KEY `account_uuid` (`uuid`),
  ADD KEY `account_title_caption` (`number`),
  ADD KEY `bank_id` (`bank_id`);

Answer 1

您正在尝试使用 .Where() lambda 表达式将 XeroBankAccount 的集合转换为 XeroBankAccount 的单个对象，这就是您遇到转换异常的原因。

如果你想得到你的查询必须返回XeroBankAccount的单个对象，那么你可以使用以下任何一种

var result = (XeroBankAccount) dbContext.XeroBankAccounts.Where(x => x.AccountUuid == tempUuid).FirstOrDefault();

或

var result = (XeroBankAccount) dbContext.XeroBankAccounts.FirstOrDefault(x => x.AccountUuid == tempUuid);

或

var result = (XeroBankAccount) dbContext.XeroBankAccounts.Where(x => x.AccountUuid == tempUuid).Take(1).SingleOrDefault();