Linq to get distinct property

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LINQ's Distinct() on a particular property 17 answers

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Rewrite your GetHashCode() function:

public int GetHashCode(MY_DATA_TABLE obj)
{
    return obj.CODE.GetHashCode();
}

Rule is, that both Equals and GetHashCode() should check the same properties, and you checking just Code in Equals() and whiole object in GetHashCode()

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另一种选择是如果Version不重要，则在每个组中进行一个组并取其中的第一个值。

var mapCodes = (from mtc in GetAllData()
                group mtc by mtc.Code into grp
                select grp.First()).ToList();

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You can use MoreLinq's DistinctBy

 var mapCodes = (from mtc in GetAllData()
                 select mtc).DistinctBy(x=>x.Code).ToList();

Or just:

var mapCodes = GetAllData().DistinctBy(x=>x.Code).ToList();

Or you can correct the GetHashCode method as mentioned in the comments

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