ASP.NET Core EF 查詢獲取導航屬性值，使用Include封裝

　　　　 // 引用 using Microsoft.EntityFrameworkCore;
        // 摘要:
        //     Specifies related entities to include in the query results. The navigation property
        //     to be included is specified starting with the type of entity being queried (TEntity).
        //     Further navigation properties to be included can be appended, separated by the
        //     '.' character.
        //
        // 參數:
        //   source:
        //     The source query.
        //
        //   navigationPropertyPath:
        //     A string of '.' separated navigation property names to be included.
        //
        // 類型參數:
        //   TEntity:
        //     The type of entity being queried.
        //
        // 返回結果:
        //     A new query with the related data included.
        public static IQueryable<TEntity> Include<TEntity>([NotNullAttribute] this IQueryable<TEntity> source, [NotNullAttribute][NotParameterized] string navigationPropertyPath) where TEntity : class;

core中提供的擴展方法Include有兩個重載方法，咱們這裏使用第一個重載方法，傳參數導航屬性名字，返回IQueryable<TEntity>，多對多導航屬性，二級導航屬性須要用‘.’點分隔符鏈接，提供完整導航屬性名稱。

下面是我封裝的擴展方法：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;

namespace System
{
    public static class IQueryableExtensions
    {
        /// <summary>
        /// 導航屬性，參數：導航屬性名稱字符串，支持多表查詢
        /// 多級導航屬性：「屬性名.屬性名」  用‘.’鏈接
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="obj"></param>
        /// <param name="Properts"></param>
        /// <returns></returns>
        public static IQueryable<T> In<T>(this IQueryable<T> obj, params string[] Properts) where T : class
        {
            IQueryable<T> data = obj;
            foreach (var prop in Properts)
            {
                data = data.Include(prop);
            }
            return data;
        }

    }
}

View Code

public class FREEFUNC
    {
        [Key]
        public long FFID { get; set; }
        public Nullable<int> SCID { get; set; }
        [ForeignKey("FUNCDEFINE")]
        public int FID { get; set; }
        public virtual FUNCDEFINE FUNCDEFINE { get; set; }
    }

public partial class FUNCDEFINE
    {
        [Key]
        public int FID { get; set; }
        public string FNAME { get; set; }
        public int CANOPR { get; set; }
        public int ISMENU { get; set; }
        public int ISEDIT { get; set; }
        public Nullable<int> FUNCTYPE { get; set; }
        [ForeignKey("FUNCDEFINE")]
        public Nullable<int> HIGHFID { get; set; }
        public string ICON { get; set; }
        public string CONTROLLER { get; set; }
        public string ACTION { get; set; }

        public virtual FUNCDEFINE HIGHF { get; set; }
    }

調用實例：

var list = FREEFUNCService.GetList().In("FUNCDEFINE", "FUNCDEFINE.HIGHF").ToList();

注：GetList()返回IQueryable<FREEFUNC>類型，IEnumerable<T>類型不支持Include方法，導航屬性必須延遲查詢時調用，最終生成連表查詢sql語句。

另外不使用Include方法也能夠獲取導航屬性，得到IQueryable對象延遲查詢，再使用.Select查詢時返回值中獲取導航屬性值，最終也會生成連表查詢，foreach不支持。

.net core ef中 獲取數據直接ToList() 導航屬性爲null。