Question

如何使用LLBLGen从DataTable加载EntityCollection或List（Of Entity）？

Answer 1

数据表将其值保存在行和列中，而LLBLGen Collection类包含一组Entity对象，这些对象表示持久存储中的表。您可以通过TypedListDAO获取使用ResultsetField定义的字段的DataTable。但是，除非您的Entity对象存储在DataTable中，否则无法从DataTable转到EntityCollection。

更有可能的是，您的DataTable中有一些键。如果是这种情况，您需要迭代DataTable的行，提取密钥并从中创建新的Entity对象。然后，您可以将这些Entity对象添加到EntityCollection。

// Define the fields that we want to get
ResultsetFields fields = new ResultsetFields(2);
fields.DefineField(EmployeeFields.EmployeeId, 0);
fields.DefineField(EmployeeFields.Name, 1);

// Fetch the data from the db and stuff into the datatable
DataTable dt = new DataTable();
TypedListDAO dao = new TypedListDAO();
dao.GetMultiAsDataTable(fields, dt, 0, null, null, null, false, null, null, 0, 0);

// We now have a datatable with "EmployeeId | Name"
// Create a new (empty) collection class to hold all of the EmployeeEntity objects we'll create
EmployeeCollection employees = new EmployeeCollection();
EmployeeEntity employee;

foreach(DataRow row in dt.Rows)
{
    // Make sure the employeeId we are getting out of the DataTable row is at least a valid long
    long employeeId;
    if(long.TryParse(row["EmployeeId"].ToString(), out employeeId)) 
    {
        // ok-looking long value, create the Employee entity object
        employee = new EmployeeEntity(employeeId);

        // might want to check if this is .IsNew to check if it is a valid object
    }
    else
    {
        throw new Exception("Not a valid EmployeeId!");
    }

    // Add the object to the collection
    employees.Add(employee);
}

// now you have a collection of employee objects...
employees.DoStuff();

LLBLGEN：从数据表中加载EntityCollection或List

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