CODEWITHSUNDEEP
c#asp.net.netlinqlambda
Steven Hu
Steven Hu

Reputation: 184

How to realize System.Linq.Expressions.Expression.Like

I am writing a dynamic linq query to realize paging, and I am now facing a problem, I need the System.Linq.Expressions.Expression.Like function, but it does not exist in System.Linq.Expressions.Expression, here is my code.

Expression mWhereFunc;          // Filter clause 
ParameterExpression mLinqParam; // Linq param

// Get current request page
string mCurPage = this.Request.QueryString["page"];
if (String.IsNullOrEmpty(mCurPage))
{
    mCurPage = "1";
}

mLinqParam = Expression.Parameter(typeof(ORD_Order), "p");
mWhereFunc = Expression.Equal(Expression.Property(mLinqParam,
     typeof(ORD_Order).GetProperty("ItemIsValid")), 
     Expression.Constant(true));

string mOrderSN = this.Request.QueryString["txtOrderSN"];
if (!String.IsNullOrEmpty(mOrderSN))
{
    mWhereFunc = Expression.And(mWhereFunc, 
     **Expression.Equal**(Expression.Property(mLinqParam,
     typeof(ORD_Order).GetProperty("OrderSN")), 
     Expression.Constant(mOrderSN)));
}

var mLambdaWhere = (Expression<Func<ORD_Order, 
      bool>>)Expression.Lambda<Func<ORD_Order, bool>>(mWhereFunc, 
     new ParameterExpression[] { mLinqParam });
Func<ORD_Order, Int32> mLambdaOrder = p => p.OrderID;

IORD_OrderRepository rptOrder = new ORD_OrderRepository();
ICTM_CustomerRepository rptCtm = new CTM_CustomerRepository();

var list = from o in rptOrder.GetAll()
             .Where(mLambdaWhere)
                 .OrderBy(mLambdaOrder)
                 .Skip((int.Parse(mCurPage) - 1) * mPageSize).Take(mPageSize)
               join c in rptCtm.GetAll()
               on o.CustomerID equals c.CustomerID
               select new
               {
                   o.OrderID,
                   o.OrderSN,
                   o.CustomerID,
                   c.ContactName,
                   o.Status,
                   o.CreateDate,
                   o.Description
               };

Expression.Equal is the place where I want to change it to Expression.Like enter image description here

Any help will be appreciated.

Upvotes: 1

Views: 1838

Answers (3)

Steven Hu
Steven Hu

Reputation: 184

I modified my code like this

mWhereFunc = Expression.And(mWhereFunc, Expression.Call(
   Expression.Property(mLinqParam, typeof(ORD_Order).GetProperty("OrderSN")), 
   typeof(String).GetMethod("Contains"), 
   new Expression[] { Expression.Constant(mOrderSN) }));

and it works, many thanks to all of you.

Upvotes: 2

the_joric
the_joric

Reputation: 12241

Like equivalents for linq are String.Contains, String.StartsWith etc. http://www.simonrhart.com/2008/06/using-like-in-linq-to-sql-under-c.html

Upvotes: 1

jorgehmv
jorgehmv

Reputation: 3713

if you are using NHibernate you can create a Like method and use a Expression to call that

You can check this post on how to do the "Like" extension here: NHibernate Linq Provider Extension

And then you build the "Like" Expression like this:

Expression.Call(typeof(MyLinqExtensions).GetMethod("IsLike"), Expression.Property(mLinqParam,
     typeof(ORD_Order).GetProperty("OrderSN")), 
     Expression.Constant(mOrderSN)));

EDIT: Just as an additional comment, you should use Expression.AndAlso instead of Expression.And since the first one is the && operator and the last one is the & operator

EDIT 2: For Entity Framework check this post (Linq To Entities scenario): SQL User-Defined Functions in Entity Framework 4, I have no experience with it but it seems the same as a NH provider, after doing that then building the Linq Expression should be the same i posted before

Upvotes: 0

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