C# Linq to Entity 多條件 OR查詢

技術背景：框架MVC，linq to Entity 須要必定的lambda書寫能力

問題：在簡單的orm中完成一些簡單的增刪查改是經過where insert delete update 完成的，可是在這個過程當中出現了一個需求：多項條件的and 和or 的組合查詢

衆所周知直接經過linq 寫的話很方便，可是咱們的框架使用了linq to entity,若是隻用lambda來寫比較複雜的and 和or 查詢就比較麻煩了。

一：簡單and 和or 查詢

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

二：複雜邏輯的and 和or 查詢

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)
 } }

這裏使用了IQuerable的擴展方法where ,表明着每一個iquerable之間爲and 關係，可是又能夠包含or 

三：複雜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); } //從新聲明一個iq，兩個iq 之間爲or 關係
        IQueryable<MemberType> iqmtwo = dbContext.MemberType; iqmtwo = iqmtwo.Where(m => m.ID > 0 || m.ID == 1); iqm = iqm.Union(iqmtwo); iqm.ToList(); } }

這裏使用了iquerable中的擴展方法union 能夠把多個iq方法合成爲一個iq ,之間爲union all  關係

第一個iq 爲一個結果集，第二個爲一個結果集，最後合併兩個結果集。

能夠知足一個sql過程當中查詢多處結果的要求，可是生成的sql仍是有點麻煩

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

最後提供一種擴展方法

四：多條件之間均爲or

/// <summary>
/// 傳入條件之間爲OR查詢 /// </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); //這兩個條件之間爲or //與iqm之間爲and //若是要與iqm之間爲or 也能夠使用union方法，可是總感受有點麻煩
        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)
 } }

我感受已經研究到這一步了索性就再往深的看一看，因而我找到了IQuerable的where 和union 的底層方法

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) })); }

只是淺薄只能看到這一步。

最後我還求助大神，大神又提出一個方案使用的是expresion方法，這個其實就是我上面提供的whereor 方法內的一樣技術，只不過我是封裝了的。

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);

應該是是要更好的方案，我只是記錄我目前理解的方法。

 最後附上關於expression的底層方法or 和 and ,提供了express語句之間可或與查詢的接口

/// <summary>
/// 用於多條件動態查詢 /// 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>
    /// 動態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>
    /// 動態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>
    /// 傳入條件之間爲OR查詢 /// </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); } }