linq to sql 多条件组合查询

引用自：http://blog.csdn.net/shandian84/article/details/8677681

 

 

//一個條件一個條件串接

using System.Linq.Expressions;
Expression<Func<ArticleList, bool>> exps = A => true;
if (GroupId != "0")
{
    Expression<Func<ArticleList, bool>> e2 = A => A.GroupId == GroupId[0];
    var invokedExpr = Expression.Invoke(e2, exps.Parameters.Cast<Expression>());
    exps = Expression.Lambda<Func<ArticleList, bool>>(Expression.And(exps.Body, invokedExpr), exps.Parameters);
}

if (TypeId != "0")
{
    Expression<Func<ArticleList, bool>> e2 = A => A.TypeId == TypeId[0];
    var invokedExpr = Expression.Invoke(e2, exps.Parameters.Cast<Expression>());
    exps = Expression.Lambda<Func<ArticleList, bool>>(Expression.And(exps.Body, invokedExpr), exps.Parameters);
}
.......................
//多欄位排序，要使用ThenBy 或 ThenByDescending
var AList = ctx.ArticleList.Where(exps).OrderBy(A => A.GroupId).ThenBy(A => A.ArticleTypeId).ThenBy(A => A.AId);

//================================================================

//一個老外寫的擴充Expression方法的靜態類別,可以解決上面冗長的程式碼
using System.Linq.Expressions;
// <summary>
/// LinqExpressions 的摘要描述
/// </summary>
public static class DynamicLinqExpressions//注意static靜態型別
{
    
    public static Expression<Func<T, bool>> True<T>() { return f => true; }
    public static Expression<Func<T, bool>> False<T>() { return f => false; }

//注意this
    public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,
                                                        Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
        return Expression.Lambda<Func<T, bool>>
              (Expression.Or(expr1.Body, invokedExpr), expr1.Parameters);
    }

    public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1,
                                                         Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
        return Expression.Lambda<Func<T, bool>>
              (Expression.And(expr1.Body, invokedExpr), expr1.Parameters);
    }

}



//==============================================================

//使用範例 
using System.Linq.Expressions;
ReadPlantDataContext ctx = new ReadPlantDataContext();
var eps = DynamicLinqExpressions.True<ArticleList>();
if (this._GroupId != "0")
 eps = eps.And(A => A.GroupId == this._GroupId[0]);
if (this._TypeId != "0")
 eps = eps.And(A => A.ArticleTypeId == this._TypeId[0]);
if (this._IsAllow != "0")
 eps = eps.And(A => A.Checked == Convert.ToBoolean(this._IsAllow));
if (this._IsCommend != "0")
 eps = eps.And(A => A.IsCommend == Convert.ToBoolean(this._IsCommend));
if (this._StartDate != DateTime.MinValue)
 eps = eps.And(A => A.AddDate >= this._StartDate);
if (this._EndDate != DateTime.MinValue)
 eps = eps.And(A => A.AddDate <= this._EndDate);
//多欄位排序，要使用ThenBy 或 ThenByDescending
var AList = ctx.ArticleList.Where(eps).OrderBy(A => A.GroupId).ThenBy(A => A.ArticleTypeId).ThenBy(A => A.AId);


Expression.invoke 参考：http://msdn.microsoft.com/en-us/library/bb355170.aspx
Lambda Expressions 参考:http://msdn.microsoft.com/en-us/library/bb397687.aspx

Expression.Lambda 参考：http://dszhang.blog.163.com/blog/static/12281257420106910952813/