如何在linq / EF Core中为where语句编写动态谓词生成器？

using System;
using System.Linq;
using System.Linq.Expressions;

public class PredicateBuilder
{
    public static Expression<Func<T, bool>> GetPredicate<T>(string propertyName, object value, string comparisonOperator)
    {
        var parameter = Expression.Parameter(typeof(T), "x");
        var property = Expression.Property(parameter, propertyName);
        var constant = Expression.Constant(value);

        Expression body;

        switch (comparisonOperator)
        {
            case "==":
                body = Expression.Equal(property, constant);
                break;
            case ">":
                body = Expression.GreaterThan(property, constant);
                break;
            case "<":
                body = Expression.LessThan(property, constant);
                break;
            case ">=":
                body = Expression.GreaterThanOrEqual(property, constant);
                break;
            case "<=":
                body = Expression.LessThanOrEqual(property, constant);
                break;
            case "!=":
                body = Expression.NotEqual(property, constant);
                break;
            default:
                throw new ArgumentException("Invalid comparison operator.");
        }

        var lambda = Expression.Lambda<Func<T, bool>>(body, parameter);
        return lambda;
    }
}

using System;
using System.Linq;

public class Program
{
    public static void Main()
    {
        var dbContext = new MyDbContext(); // 替换为你的DbContext实例

        var propertyName = "FirstName";
        var value = "John";
        var comparisonOperator = "==";

        var predicate = PredicateBuilder.GetPredicate<Customer>(propertyName, value, comparisonOperator);

        var customers = dbContext.Customers.Where(predicate).ToList();
        // 这里的Customers是你的实体集合属性，可以根据你的实际情况进行替换

        foreach (var customer in customers)
        {
            Console.WriteLine($"{customer.FirstName} {customer.LastName}");
        }
    }
}