Linq 动态表达式 多条件查询

转自

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);