c# - 使用 Entity Framework 获得结果

Question

我正在尝试查询数据库集，但在获得结果时似乎无法访问数据。这是我试过的代码。

查询#1:

public List<CustomerMain> testing()
{
        var context = new CustomerEntities();

        var query = context.CustomerMains
            .Where(p=> p.FirstName == "Thor")
            .Select(p => new CustomerMain {FirstName=p.FirstName,LastName =p.LastName}).ToList();

        return query;
}

查询#2:

public IQueryable<CustomerMain> testing()
{
        var context = new CustomerEntities();

        var query = context.CustomerMains
            .Where(p=> p.FirstName == "Thor")
            .Select(p => new CustomerMain {FirstName=p.FirstName,LastName =p.LastName});

        return query;
}

CustomerMain 是我的 DbSet，如果我运行其中任何一个并将该方法分配给 var 变量，它不会给我任何选择来获取 FirstName 或 LastName 来自变量。我发现如果我将它转换为 CustomerMain 就可以做到，但是返回查询不应该已经是 CustomerMain 类型了吗？

Answer 1

it gives me no options to grab the FirstName or LastName from the variable

因为该方法返回的是一个集合或可查询对象，而不是单个实体。您需要迭代或选择记录:

var customers = testing();
foreach (CustomerMain customer in customers)
{
    // access customer.FirstName
}

或者:

var customers = testing();
var oneCustomer = customers.FirstOrDefault(c => c.FirstName == "Thor");
// access oneCustomer.FirstName

或者，如果您希望该方法返回一条记录(如果未找到则返回 null):

public CustomerMain FindOne(string firstName)
{
    using (var context = new CustomerEntities())
    {    
        var query = context.CustomerMains.Where(p => p.FirstName == firstName);

        return query.FirstOrDefault();
    }
}