KDB: How to assign string datatype to all columns - kdb

Question

When I created the table Tab, I specified the columns as string,
Tab: ([Key1:string()] Col1:string();Col2:string();Col3:string())
But the column datatype (t) is empty. I suppose specifying the column as string has no effect.
meta Tab
c t f a
--------------------
Key1
Col1
Col2
Col3
After I do a bulk upsert in Java...
c.Dict dict = new c.Dict((Object[]) columns.toArray(new String[columns.size()]), data);
c.Flip flip = new c.Flip(dict);
conn.c.ks("upsert", table, flip);
The datatypes are all symbols:
meta Tab
c t f a
--------------------
Key1 s
Col1 s
Col2 s
Col3 s
How can I specify the datatype of the columns as string and have it remain as string?

Answer 1

You cant define a column of the empty table with as strings as they are merely lists of lists of characters
You can just set them as empty lists which is what your code is doing.
But the column will then take on the type of whatever data is inserted into it.
Real question is what is your java process sending symbols when it should be sending strings. You need to make the change there before publishing to KDB
Note if you define as chars you still wont be able to upsert strings
q)Tab: ([Key1:`char$()] Col1:`char$();Col2:`char$();Col3:`char$())
q)Tab upsert ([Key1:enlist"test"] Col1:enlist"test";Col2:enlist"test";Col3:enlist "test")
'rank
[0] Tab upsert ([Key1:enlist"test"] Col1:enlist"test";Col2:enlist"test";Col3:enlist "test")
^
q)Tab: ([Key1:()] Col1:();Col2:();Col3:())
q)Tab upsert ([Key1:enlist"test"] Col1:enlist"test";Col2:enlist"test";Col3:enlist "test")
Key1 | Col1 Col2 Col3
------| --------------------
"test"| "test" "test" "test"

Answer 2

KDB does not allow to define column types as list during creation of table. So that means you can not define your column type as String because that is also a list.
To do that only way is to define column as empty list like:
q) t:([]id:`int$();val:())
Then when you insert data to this table the column will automatically take type of that data.
q)`t insert (4;"row1")
q) meta t
c | t f a
---| -----
id | i
val| C
In your case, one option is to send string data from your Java process as mentioned by user 'emc211' or other option is to convert your data to string in KDB process before insertion.