Linq to Entity 多条件 OR查询

技术背景：框架MVC，linq to Entity 需要一定的lambda书写能力

问题：在简单的orm中完成一些简单的增删查改是通过where insert delete update 完成的，但是在这个过程中出现了一个需求：多项条件的and 和or 的组合查询

众所周知直接通过linq 写的话很方便，但是我们的框架使用了linq to entity,如果只用lambda来写比较复杂的and 和or 查询就比较麻烦了。

一：简单and 和or 查询

public void TextFoZK()
        {
            using (var dbContext = new CRMDbContext())
            {
                //第一句解析出来的sql是  select * from membertype where commercialtenantid=0 or name='住客'
                dbContext.MemberType.Where(m => m.CommercialTenantID == 0 || m.Name == "住客");
                //第二句解析出来的sql是  select * from membertype where commercialtenantid=0 and name='住客'
                dbContext.MemberType.Where(m => m.CommercialTenantID == 0 && m.Name == "住客");
            }
        }

二：复杂逻辑的and 和or 查询

public void TextFoZK(int status, string name, int commercialtenantid)
        {
            using (var dbContext = new CRMDbContext())
            {
                IQueryable<MemberType> iqm = dbContext.MemberType;
                if (status > 0)
                {
                    iqm = iqm.Where(m => m.Status == status);
                }
                if (!string.IsNullOrEmpty(name))
                {
                    iqm = iqm.Where(m => m.Name == name && m.CommercialTenantID == commercialtenantid);
                }
                iqm = iqm.Where(m => m.ID > 0 || m.ID == 1);
                iqm.ToList();
                //select * from membertype where (status=1) and (name='住客' and commercialtenantid=1) and (id>0 or id=1)
            }
        }

这里使用了IQuerable的扩展方法where ,代表着每个iquerable之间为and 关系，但是又可以包含or 

三：复杂and 和 or

public void TextFoZK(int status, string name, int commercialtenantid)
        {
            using (var dbContext = new CRMDbContext())
            {
                IQueryable<MemberType> iqm = dbContext.MemberType;
                if (status > 0)
                {
                    iqm = iqm.Where(m => m.Status == status);
                }
                if (!string.IsNullOrEmpty(name))
                {
                    iqm = iqm.Where(m => m.Name == name && m.CommercialTenantID == commercialtenantid);
                }
                //重新声明一个iq，两个iq 之间为or 关系
                IQueryable<MemberType> iqmtwo = dbContext.MemberType;
                iqmtwo = iqmtwo.Where(m => m.ID > 0 || m.ID == 1);
                iqm = iqm.Union(iqmtwo);
                iqm.ToList();
                
            }
        }

这里使用了iquerable中的扩展方法union 可以把多个iq方法合成为一个iq ,之间为union all  关系

第一个iq 为一个结果集，第二个为一个结果集，最后合并两个结果集。

可以满足一个sql过程中查询多处结果的要求，但是生成的sql还是有点麻烦

exec sp_executesql N'SELECT TOP (10) 
[Project4].[C1] AS [C1], 
[Project4].[C2] AS [C2], 
[Project4].[C3] AS [C3], 
[Project4].[C4] AS [C4], 
[Project4].[C5] AS [C5], 
[Project4].[C6] AS [C6], 
[Project4].[C7] AS [C7], 
[Project4].[C8] AS [C8], 
[Project4].[C9] AS [C9], 
[Project4].[C10] AS [C10]
FROM ( SELECT [Project4].[C1] AS [C1], [Project4].[C2] AS [C2], [Project4].[C3] AS [C3], [Project4].[C4] AS [C4], [Project4].[C5] AS [C5], [Project4].[C6] AS [C6], [Project4].[C7] AS [C7], [Project4].[C8] AS [C8], [Project4].[C9] AS [C9], [Project4].[C10] AS [C10], row_number() OVER (ORDER BY [Project4].[C1] ASC) AS [row_number]
    FROM ( SELECT 
        [Distinct1].[C1] AS [C1], 
        [Distinct1].[C2] AS [C2], 
        [Distinct1].[C3] AS [C3], 
        [Distinct1].[C4] AS [C4], 
        [Distinct1].[C5] AS [C5], 
        [Distinct1].[C6] AS [C6], 
        [Distinct1].[C7] AS [C7], 
        [Distinct1].[C8] AS [C8], 
        [Distinct1].[C9] AS [C9], 
        [Distinct1].[C10] AS [C10]
        FROM ( SELECT DISTINCT 
            [UnionAll1].[ID] AS [C1], 
            [UnionAll1].[CommercialTenantID] AS [C2], 
            [UnionAll1].[Name] AS [C3], 
            [UnionAll1].[Status] AS [C4], 
            [UnionAll1].[Discount] AS [C5], 
            [UnionAll1].[GiveIntegralScale] AS [C6], 
            [UnionAll1].[Creator] AS [C7], 
            [UnionAll1].[CreatorID] AS [C8], 
            [UnionAll1].[GMT_Create] AS [C9], 
            [UnionAll1].[GMT_Modified] AS [C10]
            FROM  (SELECT 
                [Extent1].[ID] AS [ID], 
                [Extent1].[CommercialTenantID] AS [CommercialTenantID], 
                [Extent1].[Name] AS [Name], 
                [Extent1].[Status] AS [Status], 
                [Extent1].[Discount] AS [Discount], 
                [Extent1].[GiveIntegralScale] AS [GiveIntegralScale], 
                [Extent1].[Creator] AS [Creator], 
                [Extent1].[CreatorID] AS [CreatorID], 
                [Extent1].[GMT_Create] AS [GMT_Create], 
                [Extent1].[GMT_Modified] AS [GMT_Modified]
                FROM [dbo].[commercialtenant_membertype] AS [Extent1]
                WHERE [Extent1].[CommercialTenantID] = @p__linq__0
            UNION ALL
                SELECT 
                [Extent2].[ID] AS [ID], 
                [Extent2].[CommercialTenantID] AS [CommercialTenantID], 
                [Extent2].[Name] AS [Name], 
                [Extent2].[Status] AS [Status], 
                [Extent2].[Discount] AS [Discount], 
                [Extent2].[GiveIntegralScale] AS [GiveIntegralScale], 
                [Extent2].[Creator] AS [Creator], 
                [Extent2].[CreatorID] AS [CreatorID], 
                [Extent2].[GMT_Create] AS [GMT_Create], 
                [Extent2].[GMT_Modified] AS [GMT_Modified]
                FROM [dbo].[commercialtenant_membertype] AS [Extent2]
                WHERE (0 = [Extent2].[CommercialTenantID]) AND (N''住客'' = [Extent2].[Name])) AS [UnionAll1]
        )  AS [Distinct1]
    )  AS [Project4]
)  AS [Project4]
WHERE [Project4].[row_number] > 0
ORDER BY [Project4].[C1] ASC',N'@p__linq__0 int',@p__linq__0=1

最后提供一种扩展方法

四：多条件之间均为or

/// <summary>
        /// 传入条件之间为OR查询
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source"></param>
        /// <param name="predicates"></param>
        /// <returns></returns>
        public static IQueryable<T> WhereOR<T>(this IQueryable<T> source, params Expression<Func<T, bool>>[] predicates)
        {
            if (source == null) throw new ArgumentNullException("source");
            if (predicates == null) throw new ArgumentNullException("predicates");
            if (predicates.Length == 0) return source.Where(x => false); // no matches!
            if (predicates.Length == 1) return source.Where(predicates[0]); // simple

            var param = Expression.Parameter(typeof(T), "x");
            Expression body = Expression.Invoke(predicates[0], param);
            for (int i = 1; i < predicates.Length; i++)
            {
                body = Expression.OrElse(body, Expression.Invoke(predicates[i], param));
            }
            var lambda = Expression.Lambda<Func<T, bool>>(body, param);
            return source.Where(lambda);
        }

public void TextFoZK(int status, string name, int commercialtenantid)
        {
            using (var dbContext = new CRMDbContext())
            {
                IQueryable<MemberType> iqm = dbContext.MemberType;
                if (status > 0)
                {
                    iqm = iqm.Where(m => m.Status == status);
                }
                if (!string.IsNullOrEmpty(name))
                {
                    iqm = iqm.Where(m => m.Name == name && m.CommercialTenantID == commercialtenantid);
                }
                var predicates = new List<Expression<Func<MemberType, bool>>>();
                predicates.Add(m => m.CommercialTenantID == 0 && m.Name == "住客");
                predicates.Add(m=>m.ID>0);
                //这两个条件之间为or 
                //与iqm之间为and 
                //如果要与iqm之间为or 也可以使用union方法，但是总感觉有点麻烦
                iqm = iqm.WhereOR(predicates.ToArray());
                iqm.ToList();
                //select * from membertype where (status=1) and (name='住客' and commercialtenantid=1) or (id>0 or id=1)
            }
        }

我感觉已经研究到这一步了索性就再往深的看一看，于是我找到了IQuerable的where 和union 的底层方法

 public static IQueryable<TSource> Union<TSource>(this IQueryable<TSource> source1, IEnumerable<TSource> source2)
        {
            if (source1 == null)
            {
                throw System.Linq.Error.ArgumentNull("source1");
            }
            if (source2 == null)
            {
                throw System.Linq.Error.ArgumentNull("source2");
            }
            return source1.Provider.CreateQuery<TSource>(Expression.Call(null, ((MethodInfo) MethodBase.GetCurrentMethod()).MakeGenericMethod(new Type[] { typeof(TSource) }), new Expression[] { source1.Expression, GetSourceExpression<TSource>(source2) }));
        }
 [__DynamicallyInvokable]
        public static IQueryable<TSource> Where<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
        {
            if (source == null)
            {
                throw System.Linq.Error.ArgumentNull("source");
            }
            if (predicate == null)
            {
                throw System.Linq.Error.ArgumentNull("predicate");
            }
            return source.Provider.CreateQuery<TSource>(Expression.Call(null, ((MethodInfo) MethodBase.GetCurrentMethod()).MakeGenericMethod(new Type[] { typeof(TSource) }), new Expression[] { source.Expression, Expression.Quote(predicate) }));
        }

只是浅薄只能看到这一步。

最后我还求助大神，大神又提出一个方案使用的是expresion方法，这个其实就是我上面提供的whereor 方法内的同样技术，只不过我是封装了的。

Expression<Func<MemberType, bool>> funtyps = c => c.ID > 0;
Expression<Func<MemberType, bool>> ortype = c => c.CommercialTenantID == 0 && c.Name == "住客";
funtyps = funtyps.Or(ortype);
iqmemebertype = iqmemebertype.Where(funtyps);

应该是是要更好的方案，我只是记录我目前理解的方法。

 最后附上关于expression的底层方法or 和 and ,提供了express语句之间可或与查询的接口

    /// <summary>
    /// 用于多条件动态查询
    /// zk(-_-)
    /// </summary>
    public static class PredicateBuilderUtility
    {
        public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
        {
            // build parameter map (from parameters of second to parameters of first)
            var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);
            // replace parameters in the second lambda expression with parameters from the first
            var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
            // apply composition of lambda expression bodies to parameters from the first expression 
            return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
        }
        /// <summary>
        /// 动态And
        /// </summary>
        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.AndAlso);
        }
        /// <summary>
        /// 动态Or
        /// </summary>
        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.Or);
        }
        /// <summary>
        /// 传入条件之间为OR查询
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source"></param>
        /// <param name="predicates"></param>
        /// <returns></returns>
        public static IQueryable<T> WhereOR<T>(this IQueryable<T> source, params Expression<Func<T, bool>>[] predicates)
        {
            if (source == null) throw new ArgumentNullException("source");
            if (predicates == null) throw new ArgumentNullException("predicates");
            if (predicates.Length == 0) return source.Where(x => false); // no matches!
            if (predicates.Length == 1) return source.Where(predicates[0]); // simple

            var param = Expression.Parameter(typeof(T), "x");
            Expression body = Expression.Invoke(predicates[0], param);
            for (int i = 1; i < predicates.Length; i++)
            {
                body = Expression.OrElse(body, Expression.Invoke(predicates[i], param));
            }
            var lambda = Expression.Lambda<Func<T, bool>>(body, param);
            return source.Where(lambda);
        }
       
    }