Expression instead of statement

Hope that helps I am trying to load an image and label corresponding to the table view row/cell selected by the user. The code appears in my DetailViewController implementation file as follows: , Make the data type of characterNumber as int.

this one helps. Expression trees were originally created for LINQ, which is about queries. Queries are generally function-based, so single-expression lambdas fit really well, without needing to worry about control flow within the expression tree etc. I suspect that translating expression trees for arbitrary statement lambdas into SQL etc would be a fool's errand.
Expression trees were later enhanced for .NET 4 (largely for the sake of the DLR, I believe) but the C# 4 compiler doesn't actually need to create complicated expression trees from lambda expressions for that - so it's mostly that there just isn't enough benefit for it to be worth it.

it helps some times The error message is exactly what it says. You have a lambda expression. It has a statement body. A lambda expression with a statement body can not be converted to an expression tree. But Join requires an expression tree to use with EF. You should try replacing what you have with a lambda expression that doesn't have a body like:

(cev, c) => new CustomerEventRolesModel {
                Id = cev.Id,
                CustomerId = c.Id
            }

ContactName = c.GetAttribute<string>(SystemCustomerAttributeNames.FirstName)

I wish this helpful for you Looks like the switch statement has no SQL equivelant and it's expecting to run this in Linq to Objects.
It appears that a conditional operator has a direct conversion: https://www.codeproject.com/Articles/38264/How-to-Create-T-SQL-CASE-Statements-With-LINQ-To-S

it should still fix some issue You could add a cast to for Action, although it does get a bit LISP'y with all the parentheses:

M((Action)(() => throw new Exception()));

Action thrw = () => throw new Exception();
M(thrw);