xBIM 基础14 使用LINQ实现最佳性能（优化查询）

// LINQ 表达式
var ids =
    from wall in model.Instances.OfType<IIfcWall>()
    where wall.HasOpenings.Any()
    select wall.GlobalId;

//Lambda 表达式。效果与上述的 Linq 表达式相同
var ids =
    model.Instances
    .Where<IIfcWall>(wall => wall.HasOpenings.Any())
    .Select(wall => wall.GlobalId);

public static void SelectionWithLinq()
{
    const string ifcFilename = "SampleHouse.ifc";
    var model = IfcStore.Open(ifcFilename);
    using (var txn = model.BeginTransaction())
    {
        var requiredProducts = new IIfcProduct[0]
            .Concat(model.Instances.OfType<IIfcWallStandardCase>())
            .Concat(model.Instances.OfType<IIfcDoor>())
            .Concat(model.Instances.OfType<IIfcWindow>());

        // 遍历你所需要的实体，大概有9个
        foreach (var product in requiredProducts)
        {
            // 相关业务逻辑
        }

        txn.Commit();
    }
}

public static void SelectionWithoutLinqIsSLOW()
{
    const string ifcFilename = "SampleHouse.ifc";
    var model = IfcStore.Open(ifcFilename);
    using (var txn = model.BeginTransaction())
    {
        //这种方式需要迭代大约 47309 个实体，而不是仅需要9个实体。
        foreach (var entity in model.Instances)
        {
            if (entity is IIfcWallStandardCase ||
                entity is IIfcDoor ||
                entity is IIfcWindow)
            {
                // 最好不要在这里做其他的业务逻辑
            }
        }
        txn.Commit();
    }
}