有没有办法将 DbSet 动态添加到 EF 核心并针对动态 DbSet 使用 Linq？

问题描述

我正在使用 EF Core v. 5.0 和 sqlite DB，我正在尝试将 DbSet 动态添加到我的 DbContext。我已经遵循并重新改编本指南到 EF Core：https://romiller.com/2012/03/26/dynamically-building-a-model-with-code-first/ 并且我意识到这个 DbContext 类：

     internal class GenericAppContext : DbContext
    {
        public GenericAppContext()
        {
            //disable the EF cache system to execute every running the OnModelCreating method. 
            //ATTENTION: This is a performance loss action!
            this.ChangeTracker.LazyLoadingEnabled = false;
        }

        protected override void OnConfiguring(DbContextOptionsBuilder options)
        {
            var baseDir = AppDomain.CurrentDomain.BaseDirectory;

            //if "bin" is present,remove all the exceeding path starting from "bin" word
            if (baseDir.Contains("bin"))
            {
                int index = baseDir.IndexOf("bin");
                baseDir = baseDir.Substring(0,index);
            }

            options.Usesqlite($"Data Source={baseDir}Database\\Testsqlite.db");
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            MethodInfo addMethod = typeof(ModelBuilder).getmethods().First(e => e.Name == "Entity");

            foreach (var assembly in AppDomain.CurrentDomain
              .GetAssemblies()
              .Where(a => a.GetName().Name != "EntityFramework"))
            {
                IEnumerable<Type> configTypes = assembly
                  .GetTypes()
                  .Where(t => t.BaseType != null
                    && t.BaseType.IsGenericType
                    && t.BaseType.GetGenericTypeDeFinition() == typeof(EntityTypeConfiguration<>));

                foreach (var type in configTypes)
                {
                    Type entityType = type.BaseType.GetGenericArguments().Single();

                    object entityConfig = assembly.CreateInstance(type.FullName);
                    addMethod?.MakeGenericmethod(entityType)
                      .Invoke(modelBuilder,new object[] { });
                }
            }
        }
    }

我的“博客”和“文章”类：

    internal class Blog : EntityTypeConfiguration<Blog>
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Category { get; set; }
    }

    internal class Article : EntityTypeConfiguration<Article>
    {        
        [Key]
        public int Id { get; set; }
        public string Body { get; set; }
    }

这是我如何初始化 DbContext，在“tables”变量中，我可以看到使用 context.Model.GetRelationalModel().Tables.ToList() 动态添加的“文章”表)

        public static string TestMethod()
        {  
            using (var context = new GenericAppContext())
            {
                string result = string.Empty;

                //Ensures that the database for the context exists. If it exists,no action is taken. If it does not exist then the database and all its schema are created.
                context.Database.EnsureCreated();

                List<ITable> tables = context.Model.GetRelationalModel().Tables.ToList(); 
            }
        }

此时，我成功看到动态添加的“文章”类，但是我无法使用Linq查询“文章”，当然，因为它在DbContext中并不存在.

有没有办法对像“文章”这样的动态 DbSet 添加表使用 Linq？

解决方法

最后我使用“Linq.Dynamic.Core”解决了这个问题，它允许您使用 Linq 并将 lambda 表达式编写为字符串，等等，here more info about Dynamic Linq。 >

这里是我如何修改之前显示的 TestMethod()，以及我如何对通过我的“GenericContextApp" 类。

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Dynamic.Core;
    
    public static string TestMethod()
        {  
            using (var context = new GenericAppContext())
            {
                string result = string.Empty;

                //Ensures that the database for the context exists. If it exists,no action is taken. If it does not exist then the database and all its schema are created.
                context.Database.EnsureCreated();

                IEnumerable<IEntityType> contextEntitiesList = context.Model.GetEntityTypes();
                IQueryable<IEntityType> entitiesList = contextEntitiesList.Select(p => p).ToList().AsQueryable();

                //Query against the dinamycally added "Article" table. It will return the SQL query as a string.
                result = context.Query("Your.Complete.Namespace.Article").Where("Body == \"ciao\"").ToQueryString();   

                return result;
            }
        }