jtds and dealing with nvarchar(max) and ClobImpl

[Oliver George]

Hi All

I'm experimenting with Korma querying a SQL Server database using jtds.

My select queries are coming back with net.sourceforge.jtds.jdbc.ClobImpl classes where the field is defined as nvarchar(max) where I would expect a string.  It's not terrible but an extra thing to coerce before using my results.

Below is my first hack at a solution.  I'm posting here in case there's a better way I'm missing.

The only real pain is that I need to add a transform to every (defentity ...) I define.  Perhaps there's a better way.

(defn fmap [f m]

  (into (empty m) (for [[k v] m] [k (f v)])))

(defprotocol IAsNative

  "Load data as native clojure type"

  (as-native [o]))

(extend-protocol IAsNative

  

  net.sourceforge.jtds.jdbc.ClobImpl 

  (as-native [o] (-> o (.getCharacterStream) slurp))

  

  Object 

  (as-native [o] o)

  

  nil

  (as-native [o] nil))

(defentity Users

  (pk :UserId)

  (transform (fn [m] (fmap as-native m))))

It's possible that the Microsoft driver is better.  I might be making trouble for myself by not using it.

cheers, Oliver

[Immo Heikkinen]

According to http://technet.microsoft.com/en-us/library/ms378878(v=sql.110).aspx Microsoft driver should map nvarchar(max) to String.

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[Oliver George]

Thanks.  You're right.

I setup a local maven repo and tried out the Microsoft driver.  As per that docs link it does return a string so it seems like a JTDS specific issue.

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Oliver George

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[Oliver George]

Quick follow-up for posterity.  There is an option to stop it using "lobs"...  useLobs=false

So the basic clojure.java.jdbc db config might look like:

(def db {:subprotocol "jtds:sqlserver"

         :subname "//myhost:1433/mydb"

         :user "myuser"

         :password "mypass"

         :useLobs true})

Refs

http://jtds.sourceforge.net/faq.html

http://stackoverflow.com/a/2130778/176453