C# Using Dynamic string or query in lambda expression

Question

I am trying to write a c# lambda expression with a dynamic where condition and trying to understand the type of content inside where condition. How can I call that content inside where clause dynamically?

I am taking string here for example

string query1 = "p=>p.id == 1 && p.name==\"abc\" ";
string query2 = "p=>p.id == 2 && p.name==\"def\" ";

//Normal Lambda Expression:
var details = _db.MyTable.Where(p=>p.id == 1 && p.name=="abc")

//Trying to check these if it works 
var details1 = _db.MyTable.Where(query1)

var details2 = _db.MyTable.Where(query2)

are you trying to do assignments inside your query? I don't think that will work. — littlerufe
– littlerufe, Commented May 9, 2018 at 22:10
what will be the type inside where clause? How can we dynamically assign clause? — Kurkula
– Kurkula, Commented May 9, 2018 at 22:11
How (and why) did you build that string? Might be better to fix that and go straight to building a Lambda expression. — Ian Mercer
– Ian Mercer, Commented May 9, 2018 at 22:14
I am trying to use single lambda expression by change my where condition based on few conditions. — Kurkula
– Kurkula, Commented May 9, 2018 at 22:17

dktaylor · Accepted Answer · 2018-05-09 23:02:35Z

2

Lambda expressions can use variables within their scope, so you can write it as:

int queryId = 1;
string queryName = "abc";
var details = _db.MyTable.Where(p=>p.id == queryId && p.name== queryName);

In this way you could determine what queryID and queryName were dynamically and pass them to the lambda expression. I'm also assuming you intended to check for equality with == rather than assign with =.

answered May 9, 2018 at 23:02

dktaylor

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1 Comment

Joel Coehoorn Over a year ago

Also:

if (queryId != 0) details = details.Where(p=> p.id==queryID); if (!string.IsNullOrEmpty(queryName)) details = details.Where(p => p.name == queryName);

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