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What is “the inverse side of the association” in a bidirectional JPA OneToMany/ManyToOne association
... the object, in this case the customer. The customer has no columns in the table to store the orders, so you must tell it where in the order table it can save this data (which happens via mappedBy).
Another common example are trees with nodes which can be both parents and children. In this case, th...
django syncdb and an updated model
...ngo currently does not do this automatically. Your options are:
Drop the table from the database, then recreate it in new form using syncdb.
Print out SQL for the database using python manage.py sql (appname), find the added line for the field and add it manually using alter table SQL command. (Th...
Remove Primary Key in MySQL
I have the following table schema which maps user_customers to permissions on a live MySQL database:
12 Answers
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What is the correct way to document a **kwargs parameter?
...t call out kwargs specifically. (other_silly_variable=None)
def fetch_bigtable_rows(big_table, keys, other_silly_variable=None):
"""Fetches rows from a Bigtable.
Retrieves rows pertaining to the given keys from the Table instance
represented by big_table. Silly things may happen if
other_silly_v...
Can I have multiple primary keys in a single table?
Can I have multiple primary keys in a single table?
12 Answers
12
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What is the “N+1 selects problem” in ORM (Object-Relational Mapping)?
...
SELECT
table1.*
, table2.*
INNER JOIN table2 ON table2.SomeFkId = table1.SomeId
That gets you a result set where child rows in table2 cause duplication by returning the table1 results for each child row in table2. O/R mappers sho...
Does Foreign Key improve query performance?
Suppose I have 2 tables, Products and ProductCategories. Both tables have relationship on CategoryId. And this is the query.
...
How to select from subquery using Laravel Query Builder?
...Abc::where(..)->groupBy(..); // Eloquent Builder instance
$count = DB::table( DB::raw("({$sub->toSql()}) as sub") )
->mergeBindings($sub->getQuery()) // you need to get underlying Query Builder
->count();
Mind that you need to merge bindings in correct order. If you have ot...
How to debug Lock wait timeout exceeded on MySQL?
...the query was attempting to change at least one row in one or more InnoDB tables.
Since you know the query, all the tables being accessed are candidates for being the culprit.
From there, you should be able to run SHOW ENGINE INNODB STATUS\G
You should be able to see the affected table(s)
You get a...
typecast string to integer - Postgres
I am importing data from a table which has raw feeds in Varchar, I need to import a column in varchar into a string column. I tried using the <column_name>::integer as well as to_number(<column_name>,'9999999') but I am getting errors, as there are a few empty fields, I need to retri...