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);
} }