I'm unsure of the correct format to use string and date as variables in a dynamic IQueryable
. With numbers, even though they are passed as strings, it works correctly. However, if I use strings or dates, it breaks the query without errors; it just hangs the application. I'm sure I'm missing quotes, but I can't get the format correctly.
This is my code:
string userFilter = string.Empty;
string var1 = "3";
string var2 = "54";
string var3 = "Doe, John";
DateTime var4 = DateTime.Now();
IQueryable<MyClass> query = await _context.Table.GetData();
if (!string.IsNullOrEmpty(var1))
{
userFilter = " column1 == " + var1 + " &&";
}; //This works
if (!string.IsNullOrEmpty(var2))
{
userFilter = userFilter + " column2 == " + var2 + " &&";
}; //This works
if (!string.IsNullOrEmpty(var3))
{
userFilter = userFilter + " column3 == \"" + var3 + "\" &&";
}; //Works
if (!string.IsNullOrEmpty(var4))
{
userFilter = userFilter + " column4 == " + var4 + " &&";
}; //Doesn't work
userFilter = userFilter.TrimEnd('&');
query = query.Where(userFilter);
var myData = query.ToList();
The first two 'if' work correctly, or any with numbers as strings, but actual strings or dates do not. What am I missing?
Thank you!
The System.Linq.Dynamic.Core
library uses its own syntax for DateTime
values that resembles ctor calls, like so:
context.Customers.Where("DateTimeProperty >= DateTime(2024,8,16,18,33,0)").ToList();
...but it's a better idea to use parameters, which have the form @<n>
, where <n>
is an integer:
DateTime now = DateTime.UtcNow;
context.Customers.Where("DateTimeProperty >= @0", now).ToList();
// Protip: For greater readability, define this extension method:
public static class StringExtensions
{
public static Boolean IsSet( [NotNullWhen(true)] this String? s ) => !String.IsNullOrWhiteSpace( s );
}
//
String var1 = "3";
String var2 = "54";
String var3 = "Doe, John";
DateTime var4 = DateTime.UtcNow();
IQueryable<MyClass> query = await _context.Table.GetData();
////////
if( var1.IsSet() ) query = query.Where( "column1 == @0", var1 );
if( var2.IsSet() ) query = query.Where( "column2 == @0", var2 );
if( var3.IsSet() ) query = query.Where( "column3 == @0", var3 );
query = query.Where( "column4 == @0", var4 );
////////
var myData = query.ToList();
The above query = query.Where(...)
statements will be combined as AND
terms. Whereas if you want OR
logic you can't use PredicateBuilder.Or
because these aren't Func<T,Boolean>
or Expression<Func<>>
methods, but we can hack-it with .Union
:
(Untested, YMMV)
String var1 = "3";
String var2 = "54";
String var3 = "Doe, John";
DateTime var4 = DateTime.UtcNow();
IQueryable<MyClass> q = await _context.Table.GetData();
IQueryable<MyClass> u = q.Where( "1 = 0" ); // <-- This always-false term makes it less-awkward.
////////
if( var1.IsSet() ) u = u.Union( q.Where( "column1 == @0", var1 ) );
if( var2.IsSet() ) u = u.Union( q.Where( "column2 == @0", var2 ) );
if( var3.IsSet() ) u = u.Union( q.Where( "column3 == @0", var3 ) );
u = u.Union( q.Where( "column4 == @0", var4 ) );
////////
var myData = u.ToList();