属性名称为 Lambda C# 中的表达式

Question

Updating question to be more clear on what i am trying to do here.

What i am really trying to do here is use Z.EntityFramework.Extensions to BulkMerge some data into database. Specifically i am trying to create instructions in options.ColumnInputExpression which takes the Expression i mentioned above. You can see an example here on dotnetfiddle.net/lwF8DZ

I have been working on this for few days now and can't seem to make any progress. Here is what i have.

Lets say i have Customer class.

public class Customer
{
    public int CustomerID { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public bool IsActive { get; set; }
}

And using something like this i can create a simple expression to target fields "Description" and "IsActive"

Expression<Func<Customer, object>> fieldsToUse = c => new { c.Description, c.IsActive };

This expression is exactly what i want but i must not hardcore it, instead i have to use a List such as this:

List<string> fld = new List<string>();
fld.Add("Description");
fld.Add("IsActive");

So far i have managed to use this:

public static Expression<Func<T, object>> GetExpression<T>(string propName)
{
    var arg = Expression.Parameter(typeof(T), "c");
    var property = Expression.Property(arg, propName);
    var conversion = Expression.Convert(property, typeof(object));
    var exp = Expression.Lambda<Func<T, object>>(conversion , new ParameterExpression[] { arg });
    return exp;
}

which i can call like this:

var exp = GetExpression<Customer>("IsActive");

But this only gives me following:

Expression<Func<Customer, object>> sample = c => c.IsActive;

How can i create the initial expression using what i have?

Expression<Func<Customer, object>> sample = c => new { c.Description, c.IsActive };

Any help would be appreciated. Thanks in advance!

Answer 1

You don't actually need to do what you're doing to solve the problem you're trying to solve. The bulk insert options in Z.EntityFramework.Extensions includes a ColumnInputNames property you can use instead of providing an expression. The expression syntax is probably just a convenience method that parses the expression you give it and converts it into a list of property names anyway.

context.BulkInsert(list, options => 
    options.ColumnInputNames = new List<string>{ "Name", "IsActive" });

Or, given your dynamically-generated fld list:

context.BulkInsert(list, options => options.ColumnInputNames = fld);