问题
The query I am trying to execute is similar to this:
var checksum = from i in db.Items
where i.Id == id
select SqlFunctions.Checksum("*");
However, this returns the checksum value of the string "*" rather than evaluating the wildcard. Is there a way to calculate the checksum of all the columns instead?
Update:
var checksum = db.Database.SqlQuery<int?>("SELECT CHECKSUM(*) FROM [Catalog].[Item] WHERE Id = @p0", id);
This gives me the result I want but seems dirty. Is there a way to do this without inline SQL?
回答1:
This can be done with the SqlFunctions class. This Class allows for linq-to-entities code to include methods that are easily converted to Sql.
First of all in your current edit: Using inline SQL is not 'dirty' and is totally fine in most (if not all) cases. ORMs don't provide everything, especially if there isn't a good object-column mapping that exists. However, since you're using entity framework you might as well get aquanted with the SqlFunctions static methods.
In this case there are a lot of overloads for performing a checksum, however they must all be of the same type. Since you didn't post what types your columns or how many you have, I don't want to recommend the wrong overload in an example for you to use.
Here are your options:
SqlFunctions.Checksum():
bool?char[]DateTime?DateTimeOffset?Decimal?double?Guid?TimeSpan?String
All of the above have overloads to allow up to 3 parameters (of the same type).
SqlFunctions.AggregateChecksum():
IEnumerable<int>IEnumerable<int?>
If you take a look at the documentation for these functions you'll see that the parameters that you're passing are VALUES, not column names. So you should be using them inside of a Select() clause. This is why when you passed "*" to the operation it checksummed the string containing a single asterisk instead of all columns. Also, keep in mind that these functions cannot be called directly, and must only be used within a Linq-To-Entities query.
Let's assume your columns named "ItemName" & "Description" are both strings, and you also want your id, which is an int:
var checksum = db.Items.Where(i => i.Id == id)
.Select(i => SqlFunctions.Checksum(i.Id.ToString(), i.ItemName, i.Description));
Unfortunately, as you see in the above example we had to cast our int to a string. There are no overloads that allow for different typed parameters for computing a checksum, nor are there any options that allow for more than 3 parameters in the checksum function; however, as I mentioned above sometimes you need to do an inline SQL command and this is OK.
来源：https://stackoverflow.com/questions/29547542/how-do-i-calculate-a-checksum-on-all-columns-in-a-row-using-linq-and-entity-fram