Modify MethodCallExpression Arguments (C # LINQ)
I need to add arguments to MethodCallExpression
before it gets executed for a GET request
This is an OData GET request to download all employees:
server/employees?$filter=birthday+ge+datetime'1985-01-01'
I've tried with the following code:
// My class inherits from IQToolkit which is building an expression based on the request
public class MyQueryProvider : QueryProvider
{
// Is defined in advance (after a client established a connection)
private int clientDepartmentNo;
// This is the central function, which gets a MethodCallExpression from the toolkit
// and executes it
public override object Execute(MethodCallExpression expression)
{
// The current content of expression (see my OData URL above):
// "value(NHibernate.Linq.NhQueryable`1[Models.Employee]).Where(it => (it.Birthday >= Convert(01.01.1985 00:00:00)))"
// Now I would like to extend the expression like that:
// "value(NHibernate.Linq.NhQueryable`1[Models.Employee]).Where(it => (it.Birthday >= Convert(01.01.1985 00:00:00)) && it.DepartmentNo == clientDepartmentNo)"
// That works fine
var additionalExpressionArgument = (Expression<Func<Employee, bool>>)(x => x.DepartmentNo == clientDepartmentNo);
// But that is still not possible, because the property .Arguments is readonly...
expression.Arguments.Add(additionalExpressionArgument);
// Can you give me an advice for a working solution?
// Would like to execute the query based on the URL and extension
return nHibernateQueryProvider.Execute(expression);
}
}
What should I do instead of the expression.Arguments.Add
above?
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1 answer
Assuming yours QueryProvider
is the one from here , and that hardcoding the requested object as in your question is fine for you, it should be simple:
public override object Execute(MethodCallExpression expression)
{
var query = (Query<Employee>)(CreateQuery<Employee>(expression)
.Where(x => x.DepartmentNo == clientDepartmentNo));
return nHibernateQueryProvider.Execute(query.Expression);
}
But there are probably better ways to do this, as this toolkit is here for building an expression. Forcing as I do above looks like a code smell.
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