How to create LINQ Expression Tree to select an anonymous type

Question

I would like to generate the following select statement dynamically using expression trees:

var v = from c in Countries
        where c.City == \"London\"
           


        

Answer 1

Maybe a bit late but may help to someone.

You Can generate dynamic select by call DynamicSelectGenerator in select from an entity.

public static Func DynamicSelectGenerator()
            {
                // get Properties of the T
                var fields = typeof(T).GetProperties().Select(propertyInfo => propertyInfo.Name).ToArray();

            // input parameter "o"
            var xParameter = Expression.Parameter(typeof(T), "o");

            // new statement "new Data()"
            var xNew = Expression.New(typeof(T));

            // create initializers
            var bindings = fields.Select(o => o.Trim())
                .Select(o =>
                {

                    // property "Field1"
                    var mi = typeof(T).GetProperty(o);

                    // original value "o.Field1"
                    var xOriginal = Expression.Property(xParameter, mi);

                    // set value "Field1 = o.Field1"
                    return Expression.Bind(mi, xOriginal);
                }
            );

            // initialization "new Data { Field1 = o.Field1, Field2 = o.Field2 }"
            var xInit = Expression.MemberInit(xNew, bindings);

            // expression "o => new Data { Field1 = o.Field1, Field2 = o.Field2 }"
            var lambda = Expression.Lambda>(xInit, xParameter);

            // compile to Func
            return lambda.Compile();
        }

And use by this code:

var result = dbContextInstancs.EntityClass.Select(DynamicSelectGenerator());