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Can I store a list in a database?
No, there is no “better” way to store a sequence of items in a single column. Relational databases are designed specifically to store one value per row/column combination. In order to store more than one value, you must serialize your list into a single value for storage, then deserialize it upon retrieval.
How do I sort data in SQLAlchemy?
The ORDER BY keyword lists the rows of a table as sorted by the values of a column. The DESC keyword specifies an ordering in descending order. Using the keywords together in SQLAlchemy returns an SQLAlchemy Query object with the rows sorted by the given column in descending order.
How do you store integers in a list?
Use enumerate() to add integers to a list
- a_list = [0, 0, 0]
- integers_to_add = [1, 2, 3]
- for index, integer in enumerate(integers_to_add):
- a_list[index] += integer.
- print(a_list)
How are orderable lists stored in a database?
Some variation does not use reference i.e. linked list. They choose to represent the entire order as a self-contained blob, such as a JSON-array-in-a-string [5,2,1,3,…]; such order will then be stored in a separated place. This approach also has a side effect of requiring the client side code to maintain that separated order blob.
How to re-order a list in a database?
The re-ordering would be using drag and drop and will probably be done in batches to prevent race conditions and such from the ajax requests. I’m using postgres (on heroku) if it matters. Does anyone have any ideas? Cheers for any help! First, don’t try to do anything clever with decimal numbers, because they’ll spite you.
How do you move an item in a list?
For a list of sequentially-numbered items, you can move an item up by decrementing its position and incrementing the position number of whatever the previous decrement came up with. (In other words, item 5 would become 4 and what was item 4 becomes 5, effectively a swap as Morons described in his answer.)
How much does it cost to add an item to a list?
Say you take a linked-list table approach with columns (listID, itemID, nextItemID). Inserting a new item into a list costs one insert, and one modified row. Repositioning an item costs three row modifications (the item being moved, the item before it, and the item before its new location).