1   public static IEnumerable<Customers> GetCustomersFunc1(string[] keywords)  2     {  3         DataClassesDataContext dc = new DataClassesDataContext();  4 5         //创建一个静态类型为Customers的参数表达式  6         ParameterExpression c = Expression.Parameter(typeof(Customers), "c");  7   8         //创建一个恒等于false的表达式,用于与下面的表达式取并集  9    Expression condition = Expression.Constant(false); 10         foreach (string keyword in keywords) 11          { 12             //该表达式用于判断一个Customers类的CompanyName属性的值是否包含了关键字keyword 13            Expression con = Expression.Call(   14   Expression.Property(c, typeof(Customers).GetProperty("CompanyName")), 15                typeof(string).GetMethod("Contains", new Type[]  { typeof(string) }), 16    Expression.Constant(keyword)); 17  18             //与之前的condition表达式进行逻辑或运算。 19             //如果要查找的项需要包含keywords中的所有关键字,则可使用Expression.And(con, condition)20             //并且将Expression condition = Expression.Constant(false); 21             //改成Expression condition = Expression.Constant(true); 22             condition = Expression.Or(con, condition);   23         } 24  25         //创建一个以一个Customers类作为参数并返回bool类型的委托 26   Expression<Func<Customers, bool>> end = Expression.Lambda<Func<Customers, bool>>(condition, new ParameterExpression[]  { c }); 27  28         //使用刚才构建的条件进行查询 29         var result = dc.Customers.Where(end); 30         return result; 31     } 32

1 public static IEnumerable<Customers> GetCustomersFunc2(string[] keywords)  2     { 3         //需要引用System.Linq.Dynamic。Dynamic.cs文件可在LinqSamples中找到  4   5        DataClassesDataContext dc = new DataClassesDataContext();  6         string queryString = "";  7         foreach (string keyword in keywords) 8         {  9             //原形为(c=>c.CompanyName.Contains(keyword1)) || (c=>c.CompanyName.Contains(keyword2)) ||   10             queryString += "CompanyName.Contains(\"" + keyword + "\") or "; 11         } 12  13         //与false进行逻辑或运算,为了避免queryString中最后的or出现语法错误 14         queryString += "1=0"; 15         return dc.Customers.Where(queryString); 16     } 17

1     public static IEnumerable<Customers> GetCustomersFunc3(string[] keywords)  2      {  3         //这个方法其实是伪Linq,核心还是在拼接SQL语句,所以就不多解释了  4         DataClassesDataContext dc = new DataClassesDataContext();  5         string sqlQuery = "SELECT [CustomerID], [CompanyName], [ContactName], [ContactTitle], [Address], ";  6         sqlQuery += "[City], [Region], [PostalCode],[Country], [Phone], [Fax] FROM [dbo].[Customers]  WHERE ";  7         foreach (string keyword in keywords) 8          {  9             sqlQuery += "([CompanyName] LIKE '%" + keyword + "%' ) OR "; 10         } 11         sqlQuery += "(1=0)"; 12         return dc.ExecuteQuery<Customers>(sqlQuery); 13     } 14  15