如何使用Expression获取Func <ProductModel, int> 通过特定的字符串？

Question

I have following ProductModel and dictionary for SumGetters

public class ProductModel
{
    public int Id { get; internal set; }
    public int Column1 { get; internal set; }
    public int Column2 { get; internal set; }
    public int Column3 { get; internal set; }
}

private static readonly Dictionary<string, Func<ProductModel, int>> SumGetters = new Dictionary<string, Func<ProductModel, int>>
{
    { "Column1", model => model.Column1},
    { "Column2", model => model.Column2},
    { "Column3", model => model.Column3},
};

I try to get specific column from string.

Ex. if string is Column1, then get model=>model.Column1

How to use Expression Tree to achieve this function ?

Func<ProductModel, int> sumGetter;
var isGettingSumGetter = SumGetters.TryGetValue(request.Column, out sumGetter);

Answer 1

Unclear what you are asking, BUT perhaps this is what you want:

private static readonly Dictionary<string, Func<ProductModel, int>> productModelGettersCache = new Dictionary<string, Func<ProductModel, int>>();

public static Func<ProductModel, int> GetGetter(string column)
{
    Func<ProductModel, int> getter;

    if (!productModelGettersCache.TryGetValue(column, out getter))
    {
        var par = Expression.Parameter(typeof(ProductModel));
        var exp = Expression.Lambda<Func<ProductModel, int>>(Expression.Property(par, column), par);
        getter = exp.Compile();
    }

    return getter;
}

Note that creating and compiling an expression tree is "slow", so I'm caching the created expressions. If you only want the expression tree before compilation, then you can find it in exp .