Linq to Entity Group By error 无法翻译答案

【问题标题】：Linq to Entity Group By error can't translateLinq to Entity Group By error 无法翻译
【发布时间】：2021-11-06 13:02:03
【问题描述】：

我尝试做这个查询：

var query = from cont in _gpiContext.Contacto
                        join per in _gpiContext.Persona on cont.IdPersona equals per.IdPersona
                        where cont.IdCliente == idCliente
                        && cont.IdTipoContacto == tipoContacto.IdTipoContacto
                        group new { cont, per } by new { cont.IdCliente, cont.IdContacto, cont.IdPersona } into g
                        select new Representante
                        {
                            IdContacto = g.Key.IdContacto,
                            IdCliente = g.Key.IdCliente,
                            IdPersona = g.Key.IdPersona,
                            Nombre = g.First().per.Nombre
                        };
return await query.ToListAsync();

我已经尝试了所有方法，但无法找出问题所在，我有非常相似的查询并且它们确实完美无缺。我不想做客户评估。

但我得到以下错误：

"LINQ 表达式 'GroupByShaperExpression: KeySelector: new { IdCliente = (Nullable)c.ID_CLIENTE, IdContacto = c.ID_CONTACTO, IdPersona = (Nullable)c.ID_PERSONA }, ElementSelector:new { con = EntityShaperExpression：实体类型：联系人值缓冲区表达式： ProjectionBindingExpression: con IsNullable: 假 , 每 = EntityShaperExpression：实体类型：角色值缓冲区表达式： ProjectionBindingExpression：每 IsNullable: 真 } .Select(s => s.per.Nombre) .First()' 无法翻译。要么以可翻译的形式重写查询，要么显式切换到客户端评估通过插入对“AsEnumerable”、“AsAsyncEnumerable”、“ToList”的调用，或“ToListAsync”。见https://go.microsoft.com/fwlink/?linkid=2101038 了解更多信息。”

我的实体：联系方式

// <auto-generated> This file has been auto generated by EF Core Power Tools. </auto-generated>
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using Microsoft.EntityFrameworkCore;

#nullable disable

namespace GpiWebApp.Data.Gpi
{
    [Table("CONTACTO")]
    public partial class Contacto
    {
        [Key]
        [Column("ID_CONTACTO", TypeName = "numeric(10, 0)")]
        public decimal IdContacto { get; set; }
        [Column("ID_CLIENTE", TypeName = "numeric(10, 0)")]
        public decimal? IdCliente { get; set; }
        [Column("ID_TIPO_CONTACTO", TypeName = "numeric(10, 0)")]
        public decimal? IdTipoContacto { get; set; }
        [Column("ID_PERSONA", TypeName = "numeric(10, 0)")]
        public decimal? IdPersona { get; set; }

        [ForeignKey(nameof(IdCliente))]
        [InverseProperty(nameof(Cliente.Contacto))]
        public virtual Cliente IdClienteNavigation { get; set; }
        [ForeignKey(nameof(IdPersona))]
        [InverseProperty(nameof(Persona.Contacto))]
        public virtual Persona IdPersonaNavigation { get; set; }
        [ForeignKey(nameof(IdTipoContacto))]
        [InverseProperty(nameof(TipoContacto.Contacto))]
        public virtual TipoContacto IdTipoContactoNavigation { get; set; }
    }
}

角色

// <auto-generated> This file has been auto generated by EF Core Power Tools. </auto-generated>
    using System;
    using System.Collections.Generic;
    using System.ComponentModel.DataAnnotations;
    using System.ComponentModel.DataAnnotations.Schema;
    using Microsoft.EntityFrameworkCore;
    
    #nullable disable
    
    namespace GpiWebApp.Data.Gpi
    {
        [Table("PERSONA")]
        public partial class Persona
        {
            public Persona()
            {
                Cliente = new HashSet<Cliente>();
                Contacto = new HashSet<Contacto>();
                DireccionPersona = new HashSet<DireccionPersona>();
                EmailPersona = new HashSet<EmailPersona>();
                TelefonoPersona = new HashSet<TelefonoPersona>();
            }
    
            [Key]
            [Column("ID_PERSONA", TypeName = "numeric(10, 0)")]
            public decimal IdPersona { get; set; }
            [Required]
            [Column("TIPO_ENTIDAD")]
            [StringLength(1)]
            public string TipoEntidad { get; set; }
            [Column("NOMBRE")]
            [StringLength(100)]
            public string Nombre { get; set; }
            [Column("PATERNO")]
            [StringLength(50)]
            public string Paterno { get; set; }
            [Column("MATERNO")]
            [StringLength(50)]
            public string Materno { get; set; }
            [Column("SEXO")]
            [StringLength(1)]
            public string Sexo { get; set; }
            [Column("FECHA_NACIMIENTO", TypeName = "datetime")]
            public DateTime? FechaNacimiento { get; set; }
            [Required]
            [Column("IDENTIFICADOR")]
            [StringLength(12)]
            public string Identificador { get; set; }
            [Required]
            [Column("TIPO_IDENTIFICADOR")]
            [StringLength(1)]
            public string TipoIdentificador { get; set; }
            [Column("COD_PAIS")]
            [StringLength(3)]
            public string CodPais { get; set; }
            [Column("ID_ESTADO_CIVIL", TypeName = "numeric(3, 0)")]
            public decimal? IdEstadoCivil { get; set; }
            [Column("PROFESION")]
            [StringLength(20)]
            public string Profesion { get; set; }
            [Column("TELEFONO")]
            [StringLength(50)]
            public string Telefono { get; set; }
            [Column("CELULAR")]
            [StringLength(50)]
            public string Celular { get; set; }
            [Column("EMAIL")]
            [StringLength(50)]
            public string Email { get; set; }
            [Column("EMPLEADOR")]
            [StringLength(50)]
            public string Empleador { get; set; }
            [Column("CARGO")]
            [StringLength(50)]
            public string Cargo { get; set; }
            [Column("FLG_MAYOR_EDAD")]
            [StringLength(1)]
            public string FlgMayorEdad { get; set; }
            [Column("ID_TIPO_ESTADO", TypeName = "numeric(4, 0)")]
            public decimal? IdTipoEstado { get; set; }
            [Column("COD_ESTADO")]
            [StringLength(3)]
            public string CodEstado { get; set; }
            [Column("GIRO")]
            [StringLength(100)]
            public string Giro { get; set; }
            [Column("ID_TIPO_SOCIEDAD", TypeName = "numeric(3, 0)")]
            public decimal? IdTipoSociedad { get; set; }
            [Column("DSC_DOCUMENTO")]
            [StringLength(20)]
            public string DscDocumento { get; set; }
            [Column("OBSERVACIONES")]
            [StringLength(150)]
            public string Observaciones { get; set; }
            [Column("COPIA_ESCRITURA")]
            [StringLength(1)]
            public string CopiaEscritura { get; set; }
            [Column("FECHA_FORMACION", TypeName = "datetime")]
            public DateTime? FechaFormacion { get; set; }
            [Column("LUGAR")]
            [StringLength(80)]
            public string Lugar { get; set; }
            [Column("NOTARIA")]
            [StringLength(100)]
            public string Notaria { get; set; }
            [Column("REGISTRO")]
            [StringLength(100)]
            public string Registro { get; set; }
            [Column("NUMERO")]
            [StringLength(100)]
            public string Numero { get; set; }
            [Column("ANO")]
            [StringLength(100)]
            public string Ano { get; set; }
            [Column("ANTECEDENTES")]
            [StringLength(1)]
            public string Antecedentes { get; set; }
            [Column("SITIOWEB")]
            [StringLength(50)]
            public string Sitioweb { get; set; }
    
            [ForeignKey(nameof(CodPais))]
            [InverseProperty(nameof(Pais.Persona))]
            public virtual Pais CodPaisNavigation { get; set; }
            [ForeignKey(nameof(IdEstadoCivil))]
            [InverseProperty(nameof(EstadoCivil.Persona))]
            public virtual EstadoCivil IdEstadoCivilNavigation { get; set; }
            [ForeignKey(nameof(IdTipoSociedad))]
            [InverseProperty(nameof(TipoSociedad.Persona))]
            public virtual TipoSociedad IdTipoSociedadNavigation { get; set; }
            [InverseProperty("IdPersonaNavigation")]
            public virtual ICollection<Cliente> Cliente { get; set; }
            [InverseProperty("IdPersonaNavigation")]
            public virtual ICollection<Contacto> Contacto { get; set; }
            [InverseProperty("IdPersonaNavigation")]
            public virtual ICollection<DireccionPersona> DireccionPersona { get; set; }
            [InverseProperty("IdPersonaNavigation")]
            public virtual ICollection<EmailPersona> EmailPersona { get; set; }
            [InverseProperty("IdPersonaNavigation")]
            public virtual ICollection<TelefonoPersona> TelefonoPersona { get; set; }
        }
    }

感谢您的建议！

【问题讨论】：

我想知道它是从哪里来的tipoContacto.IdTipoContacto？

标签： c# entity-framework-core linq-to-entities

【解决方案1】：

为什么不试试这个

....
group new { cont, per } by new { cont.IdCliente, cont.IdContacto, cont.IdPersona, per.Nombre } into g
  select new Representante
    {
     IdContacto = g.Key.IdContacto,
       IdCliente = g.Key.IdCliente,
       IdPersona = g.Key.IdPersona,
       Nombre = g.Key.Nombre
      };

【讨论】：

他们为什么不试试呢？嗯，这是一个完全不同的分组。 OP 不想按Nombre 分组。又是一个冲动的答案，你过早地假设 OP 会像那样改变他们的要求。当然，这里唯一正确的答案是 EF 不支持它，他们必须找到解决方法。

【解决方案2】：

Serge's answer 应该适用于这种特殊情况，但我想在您尝试在 LINQ 中使用分组做更复杂的事情之前，我会添加一些上下文。

查看 EFCore 文档中的 Complex query operators 部分。特别有趣的是他们说的部分：

由于没有数据库结构可以表示 IGrouping，因此 GroupBy 运算符在大多数情况下没有翻译。

这是有道理的，因为如果您用 SQL 术语来思考，那么您可以对 GROUP BY 进行的聚合很少，例如总和、计数、平均值、最小值、最大值；但是没有 FIRST 或 LAST（除非您进入分区和排名，这类似于分组，但实际上并非如此）。

所以，长话短说，您的查询实际上是有效的 LINQ。如果您尝试将其应用于List<>，它将起作用。但它永远无法翻译成服务器端的 SQL。

【讨论】：