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## XPO对象类中字段值通过运算后存入数据库中 ##

第一种不存入数据库，临时运算

[DisplayName("字段")]
public double CoalNum; 

private double _SO2; 
[DisplayName("SO2")，NonPersistent]
public double SO2 {
    get { return _SO2; }
    set {
        _SO2 = (CoalNum * 0.012 * 0.8 * 2);
    }
}

第二种字段存入数据库；但是运算过后数据会延迟存入数据库

[DisplayName("字段")]
public double CoalNum; 

private double _SO2; 
[DisplayName("SO2")]

public double SO2 {
    get { return _SO2 = (CoalNum * 0.012 * 0.8 * 2); }  
}

第三种都同时存入数据库

[DisplayName("字段")]
public double CoalNum; 

[DisplayName("SO2")]
public double SO2; 

protected override void OnSaving(){
    SO2 = (CoalNum * 0.012 * 0.8 * 2);
}