在现有SQLite记录中更新BLOB字段的语法？

Question

What is the syntax to UPDATE a BLOB field in an existing SQLite record, using Python? I create a 13x13 array of floats and want to Update a specific record (ie using a WHERE clause) in my table with that array.

What is the proper UPDATE syntax?

The array has the following form:

[ 4.65640926e+00  5.59250259e+00  5.28963852e+00  1.60680866e+00
  -3.39492680e-01 -4.76834650e-01 -4.76834650e-01 -2.29132240e-01
   1.49733067e+00  1.51563072e+00  1.49733067e+00  9.53471420e-01
  -1.40306473e+00]

 [ 5.28963852e+00  5.34537315e+00  5.05013466e+00  1.48362923e+00
  -3.69843300e-01 -4.76834650e-01 -4.76834650e-01 -2.29132240e-01
   7.60705290e-01  1.49733067e+00  9.53471420e-01  3.05504260e-01
  -1.40306473e+00]

Totaling 13 rows of 13 sub-arrays.

Thank you, Bill

Answer 1

The syntax for the SQL is :-

UPDATE mytable SET myblobcolumn = x'ffeedd' WHERE your_where_clause;

Where

• mytable is the table name,
• myblobcolumn is the name of the column that is to be updated,
• your_where_clause is the selection criteria,
• x'ffeedd' is the byte array value, converted to hexadecimal, that is to be used to update the column.

Obviously the above are only representations, you would have to substitute appropriate values

• SQL As Understood By SQLite - UPDATE

• Datatypes In SQLite Version 3

Answer 2

A friend pointed me to this solution, which works nicely. The original answer was from StackOverflow, to give proper credit.

def adapt_array(arr): """ Reformat a numpy array so as to be writeable to SQLite BLOB fields Input: Numpy Array Returns: formatted Binary BLOB compatable Code Source: Python insert numpy array into sqlite3 database """ out = io.BytesIO() np.save(out, arr) out.seek(0) return sqlite3.Binary(out.read())

def convert_array(text): """ Reformat a SQLite BLOB field into the originating Numpy array Input: Numpy BLOB from SQLite Returns: numpy array Code Source: Python insert numpy array into sqlite3 database """ out = io.BytesIO(text) out.seek(0) return np.load(out)