Dynamic distinct values using Linq to SQL

Question

I was unsure if what I wrote as a Title would suffice, but I will do my best to explain what I am trying to accomplish here:

I am trying to recreate this query that I use to look up distinct data from TestColumn:

 List<string> groupQuery = (from p in testDepo
                                      group p by new { p.TestColumn}
                                      into distinctTest
                                      select distinctTest.First().TestColumn).ToList();

But instead of statically call TestColumn. I would like to dynamically pass in the name: TestColumn into a variable and then do my distinct value query using the variable name.

So far I have this:

string primaryColumn = "TestColumn"
List<string> groupQuery= (from p in testDepo
                                    group p by new { primaryColumn }
                                    into distinctTest
                                    select distinctTest.First().GetType().GetProperty(primaryColumn).GetValue(distinctTest.First()).ToString()).ToList();

I know i am probably doing something silly, but i cant quite wrap my head around it right now. my dynamic query only half works. It is only getting the first distict value, but not the rest of them. Can anyone help me out?

p is the object that i am trying get distinct values from. — scapegoat17
– scapegoat17, Commented Apr 24, 2015 at 20:36
Like my entity model that is connected to my database to a table called Test — scapegoat17
– scapegoat17, Commented Apr 24, 2015 at 20:54
Nice coincidence, I just named the test class in my code Test just like your table name. — david.s
– david.s, Commented Apr 24, 2015 at 21:08

ΩmegaMan · Accepted Answer · 2015-04-25 12:10:23Z

4

You can create a Func from an Expression using your property column string like this:

var primaryColumn = "TestColumn";
var param = Expression.Parameter(typeof(Test), "p");
var col = Expression.Property(param, primaryColumn);
var lambda = Expression.Lambda(col, param);
var func = lambda.Compile();

Then use it in your query like this:

List<string> groupQuery= (from p in testDepo
                          group p by func.DynamicInvoke(p)
                          into distinctTest
                          select distinctTest.First()
                                             .GetType()
                                             .GetProperty(primaryColumn)
                                             .GetValue(distinctTest.First())
                                             .ToString()
                          ).ToList()

edited Apr 25, 2015 at 12:10

ΩmegaMan

32.2k13 gold badges110 silver badges138 bronze badges

answered Apr 24, 2015 at 20:27

david.s

11.4k6 gold badges54 silver badges83 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

scapegoat17 Over a year ago

for var p = Expression.Parameter(typeof(Test), "p"); i would not be able to use p since it is already being used in my query. Would i have to change both the variable name and the string name? or just the variable name?

david.s Over a year ago

Change just the variable name. I fixed the answer.

jdweng · Accepted Answer · 2015-04-24 20:18:54Z

0

What is TestDepro? You need to be able to return the column by name something like p[primaryColumn].

answered Apr 24, 2015 at 20:18

jdweng

34.5k3 gold badges17 silver badges19 bronze badges

Collectives™ on Stack Overflow

Dynamic distinct values using Linq to SQL

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related