Dynamic Expression

[devoas]

Hi,

Please guide the recommended way to join Dynamic expressions. Basically we have different selection criterias
Like
[ ] By Transaction ID:  ________        (.) And    ( ) Or
[ ] By Customer ID : __________        (.) And    ( ) Or
[ ] By Date : _________                      (.) And    ( ) Or
.
.

for this we prepare different Dynamic expressions based on user selection like following.

  

 

 

Expression <Func<SalesMaster, bool>> predicatex = c=>c.TranNumb ==2;

Expression<Func<SalesMaster, bool>> predicatey = c=>c.CustomerId ==2;

 

Now Please recommend how can I Join multiple predicates based on AND/OR operation and apply in single Where Cluase. 

currently we are using following approach...

var query = from p in scope.Extent<SalesMaster>().Where(predicatex)
                  select p;
query = query.Where(predicatex);
query = query.Where(predicatey);

var result = query.ToList();

But this approach does allow us to use OR  all these clauses generate AND

I tried to join predicates using Expression.And and Expression.Or  but resultant predicate is compile and throwing exception as posted previously.

Please Help...

Thanks,
devoas,

[Jordan]

Hi devoas,

You can easily combine multiple lambda expressions with the code bellow:

Expression<Func<Customer, bool>> filter1 = c => c.City.StartsWith("S");
Expression<Func<Customer, bool>> filter2 = c => c.City.StartsWith("M");
Expression<Func<Customer, bool>> filter3 = c => c.ContactTitle == "Owner";

Expression<Func<Customer, bool>>[] filterExpressions = new Expression<Func<Customer, bool>>[] { filter1, filter2, filter3 };
Func<Expression, Expression, BinaryExpression>[] operators = new Func<Expression, Expression, BinaryExpression>[] { Expression.OrElse , Expression.AndAlso};
Expression<Func<Customer, bool>> filter = null;
if (filterExpressions.Length > 0)
{
    Expression body = filter1.Body;
    for (int i = 1; i < filterExpressions.Length; i++)
    {
        body = operators[i - 1](body, filterExpressions[i].Body);
    }
    filter = Expression.Lambda<Func<Customer, bool>>(body, filter1.Parameters);
}

IObjectScope objectScope = ObjectScopeProvider1.GetNewObjectScope();
IQueryable<Customer> query = (from c in objectScope.Extent<Customer>() select c).Where(filter);

Notice that the Expression methods used are OrElse and AndAlso. They produce binary expressions.
The And and Or methods produce bitwise operations.

The result lambda expression will look like this:
filter = {c => ((c.City.StartsWith("S") || c.City.StartsWith("M")) && (c.ContactTitle = "Owner"))}

And the generated SQL will look like this:
"SELECT [CustomerID] AS COL1, [Address] AS COL2, [City] AS COL3, [CompanyName] AS COL4, [ContactName] AS COL5, [ContactTitle] AS COL6, [Country] AS COL7, [Fax] AS COL8, [Phone] AS COL9, [PostalCode] AS COL10, [Region] AS COL11 FROM [Customers] WHERE ([City] LIKE 'S%' OR [City] LIKE 'M%') AND [ContactTitle] = 'Owner' "

I hope this helps.
Do not hesitate to write again if you have more questions or suggestions.

Best wishes,
Jordan
the Telerik team

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