C# 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 ==  || 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 ==  && 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 > )
        {
            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 >  || m.ID == );
        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 > )
        {
            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 >  || m.ID == );
        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 == ) return source.Where(x => false); // no matches!
    if (predicates.Length == ) return source.Where(predicates[]); // simple

    var param = Expression.Parameter(typeof(T), "x");
    Expression body = Expression.Invoke(predicates[], param);
    for (int i = ; 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 > )
        {
            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 ==  && m.Name == "住客");
        predicates.Add(m=>m.ID>);
        //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 > ;
Expression<Func<MemberType, bool>> ortype = c => c.CommercialTenantID ==  && 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 == ) return source.Where(x => false); // no matches!
        if (predicates.Length == ) return source.Where(predicates[]); // simple

        var param = Expression.Parameter(typeof(T), "x");
        Expression body = Expression.Invoke(predicates[], param);
        for (int i = ; 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);
    }

}