如何在C＃中比较/转换SQL rowversion字段数据

Question

I have two records in my student table with a row-version field. I am creating the object of that record as student class in my C# code.

My question are:

1. In which C# compatible datatype is rowversion data cast?
2. How do I compare rowversion of two records and find which one is the latest in C#?

Answer 1

One way to find the latest rowversion is to use the StructuralComparer

var r1 = new byte[] {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10, 0x00};
var r2 = new byte[] {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x09, 0xFF};

bool r1_is_newer = StructuralComparisons.StructuralComparer.Compare(r1, r2) > 0;

A benefit of the structural comparisons is that they automatically deal with NULL s

Regarding use of the BitConverter . If the above byte arrays were converted to UInt64 using the BitConverter , you'd end up with very high numbers and the comparison is meaningless (as the rowversion changes by one, the uint64 converted number changes by around 2^56)

If you'd like to sprinkle some LINQ over it to make it extra slow, you can use

bool r1_is_newer = 
  Enumerable.Zip(r1, r2, (b1, b2) => new { b1, b2 })
  .SkipWhile(item => item.b1 == item.b2)
  .Take(1).Any(item => item.b1 > item.b2);

Answer 2

rowversion is binary(8) , and will be returned as a byte[] if you use SqlCommand / SqlDataReader . If you use EF 4.1, the corresponding property will also be byte[] .

You could use BitConverter to convert to UInt64 and then compare. You could also return the rowversion cast as bigint from SQL Server, which would appear as a long in C#. In either case, the larger value would have been created later.

In my own tests, I've seen that rowversion starts at a small, positive value (not 0). If you do cast to bigint , you'll have to consider what will happen when it reaches 2^64 . In my case, it's not something I have to worry about. If you think that will happen in your database, then you'll have to add logic to handle that in your comparison, or just stick with BitConverter.ToUInt64 .

Also, be careful if your rowversion column accepts NULL ; You'll have to account for that if it does.