数据库接口的动态可查询参数

根据评论，我提供了两个选项。

1. 基于给用户的一组选项。使用TreeExpression动态地构建表达式，就像上面的例子(这个例子确实太简单了，但是你可以有一个想法)。

   ParameterExpression numParam = Expression.Parameter(typeof(int), "num");
   ConstantExpression five = Expression.Constant(5, typeof(int));
   BinaryExpression numLessThanFive = Expression.LessThan(numParam, five);
   Expression<Func<int, bool>> lambda1 = Expression.Lambda<Func<int, bool>>(numLessThanFive, new ParameterExpression[] { numParam });
   

这个链接会给你更多关于这个主题的信息:https://msdn.microsoft.com/en-us/library/bb882637.aspx

为了让用户键入一些表达式并将其转换为查询，搜索Antlr http://www.antlr.org/或类似的工具，允许您想要实现的表达式语法并使用1º解决方案来构建表达式。

我的示例代码如下:您需要安装以下包…

install-package entityframework
install-package newtonsoft.json

请注意，通过插入有效的VB，这段代码很容易被注入。

我将代码编译成30742268.exe，您可以看到它被添加为IContext接口的参考，等等。

using System;
using System.Linq;
using System.Text;
using Microsoft.VisualBasic;
using System.CodeDom.Compiler;
using Model;
using System.Collections.Generic;
using System.Data.Entity;
using Newtonsoft.Json;
namespace _30742268 {
    class Program {
        const String queryWrapperCode = @"
            Imports System.Linq
            Imports System.Data.Entity
            Imports Model
            Public Class DynamicQuery
                Implements IDynamicQuery
                Public Function Run(data As IContext) As IQueryable Implements IDynamicQuery.Run
                    Return {0}
                End Function
            End Class
        ";
        static void Main(String[] args) {
            using (var provider = new VBCodeProvider()) {
                var parameters = new CompilerParameters();
                parameters.ReferencedAssemblies.Add("System.Core.dll");
                parameters.ReferencedAssemblies.Add("EntityFramework.dll");
                parameters.ReferencedAssemblies.Add("30742268.exe");
                parameters.GenerateInMemory = true;
                Console.WriteLine("Enter LINQ queries, 'demo' for an example, 'exit' to stop:");
                for (;;) {
                    try {
                        var dynamicQueryString = Console.ReadLine();
                        if (dynamicQueryString == "exit")
                            return;
                        if (dynamicQueryString == "demo")
                            Console.WriteLine(dynamicQueryString = "from person in data.People where person.Name.Length = 4");
                        var results = provider.CompileAssemblyFromSource(parameters, String.Format(queryWrapperCode, dynamicQueryString));
                        if (results.Errors.HasErrors) {
                            var sb = new StringBuilder();
                            foreach (CompilerError error in results.Errors) {
                                sb.AppendLine(String.Format("Error ({0}): {1}", error.ErrorNumber, error.ErrorText));
                            }
                            throw new InvalidOperationException(sb.ToString());
                        }
                        var assembly = results.CompiledAssembly;
                        var assemblyType = assembly.GetTypes().Single(x => typeof (IDynamicQuery).IsAssignableFrom(x));
                        var constructorInfo = assemblyType.GetConstructor(new Type[] {});
                        var dynamicQuery = (IDynamicQuery) constructorInfo.Invoke(null);
                        using (var context = new Context()) {
                            dynamic result = dynamicQuery.Run(context);
                            foreach (var person in result)
                                Console.WriteLine(person);
                        }
                    }
                    catch (Exception exception) {
                        Console.WriteLine(exception);
                    }
                }
            }
        }
    }
}
namespace Model {
    public interface IDynamicQuery {
        IQueryable Run(IContext context);
    }
    public abstract class Entity {
        public override String ToString() {
            return JsonConvert.SerializeObject(this, Formatting.Indented, new JsonSerializerSettings { ReferenceLoopHandling = ReferenceLoopHandling.Ignore });
        }
    }
    public class Person : Entity {
        public Int64 Id { get; protected set; }
        public String Name { get; set; }
        public virtual Home Home { get; set; }
    }
    public class Home : Entity {
        public Int64 Id { get; protected set; }
        public String Address { get; set; }
        public virtual ICollection<Person> Inhabitants { get; set; } 
    }
    public interface IContext {
        IQueryable<Person> People { get; set; }
        IQueryable<Home> Homes { get; set; }
    }
    public class Context : DbContext, IContext {
        public virtual DbSet<Person> People { get; set; }
        public virtual DbSet<Home> Homes { get; set; }
        IQueryable<Person> IContext.People {
            get { return People; }
            set { People = (DbSet<Person>)value; }
        }
        IQueryable<Home> IContext.Homes {
            get { return Homes; }
            set { Homes = (DbSet<Home>)value; }
        }
        public Context() {
            Configuration.ProxyCreationEnabled = false;
            Database.SetInitializer(new ContextInitializer());
        }
    }
    class ContextInitializer : DropCreateDatabaseAlways<Context> {
        protected override void Seed(Context context) {
            var fakeSt = new Home {Address = "123 Fake St."};
            var alabamaRd = new Home {Address = "1337 Alabama Rd."};
            var hitchhikersLn = new Home {Address = "42 Hitchhiker's Ln."};
            foreach (var home in new[] {fakeSt, alabamaRd, hitchhikersLn})
                context.Homes.Add(home);
            context.People.Add(new Person { Home = fakeSt       , Name = "Nick" });
            context.People.Add(new Person { Home = fakeSt       , Name = "Paul" });
            context.People.Add(new Person { Home = fakeSt       , Name = "John" });
            context.People.Add(new Person { Home = fakeSt       , Name = "Henry" });
            context.People.Add(new Person { Home = alabamaRd    , Name = "Douglas" });
            context.People.Add(new Person { Home = alabamaRd    , Name = "Peter" });
            context.People.Add(new Person { Home = alabamaRd    , Name = "Joshua" });
            context.People.Add(new Person { Home = hitchhikersLn, Name = "Anne" });
            context.People.Add(new Person { Home = hitchhikersLn, Name = "Boris" });
            context.People.Add(new Person { Home = hitchhikersLn, Name = "Nicholes" });
            context.People.Add(new Person { Home = hitchhikersLn, Name = "Betty" });
            context.SaveChanges();
        }
    }
}