I am trying to create an event that searches a string (i.e. Operation) from a database returns corresponding equipment capable of doing that operation. However, when I try to add the resulting equipment into a collection col_EquipmentToDo of type Equipment it gives an error saying "Incompatible operand types Main.equipments_Population and String." I tried to match the resulting string from the database (i.e. Equipment) to the population that I initially created but it doesn't work.
Heres the code:
int numOperationsToDo = col_OperationsToDo.size();
for (int i=0; i<numOperationsToDo; i++) {
ReqOperation=col_OperationsToDo.get(0);
variable=selectFrom(toperation_per_tool)
.where(toperation_per_tool.operation.eq(ReqOperation))
.uniqueResult(toperation_per_tool.tool_reference);
col_MachinesToDo.addLast(main.pop_equipments==variable);
}
Your database entry is a String (i.e. a literal word such as "myEquipment12"). Your collection is not. It expects elements of type Equipment, i.e. actual agents of that type.
So either change the collection to a list of Strings or use the String from the database, create an Equipment agent from it (or find an existing agent matching it) and add that to your collection.
Which one to use depends on your model.
PS: Before you ask: You cannot store Equipment agents in a dbase, only String names :)
Related
I am using Parse which has an preload User table in the database. I want from each user a unique userId (Int). Parse's objectId is unique but not an Int and username is a String. Username is unique for each user , so can I somehow convert each username into a number ?
I tried .toInt() , Int() but I got nothing.
WHY :
I have an existing table with user's ratings (movies) and I want to extent this table with more ratings. The userId field is a Number value so I must keep it this way.
Swift String has a hash property. It also conforms to the Hashable protocol. Maybe you can use that.
However, hashValue has the following comment:
Axiom:x == y implies x.hashValue == y.hashValue.
Note: The hash value
is not guaranteed to be stable across different invocations of the
same program. Do not persist the hash value across program runs.
so, use carefully...
Note: as stated in the comments, the hashValue is not guaranteed to be unique, but collisions should be rare, so it may be a solution anyway.
Having unique arbitrary String to Int map is not possible. You have to put some constraints on the allowed characters and string length. However, even if you use case-insensitive alpha-numeric user names, with some smart variable-length bit-encoding, then you look at some 5 bits per character on rough average. 64-bit integer can accomodate up to some 12 characters this way. Longer than that, you will inevitably have collisions.
I think you approach the problem from the wrong end. Instead of having a function for String -> Int mapping, what stops you from having a separate table with Int <-> String mapping? Just have some functionality that will check whether a userID exists in that table, and if it does not, then insert a new record for such userID and assign a new unique number to it. This way it will take quite some time and service popularity to deplete 64-bit integer capacity.
I have a field in table in next format 1_2..1_10|1_6|1_8| where 1_2..1_10 include 1_2, 1_3 and other.
How I can select data, where number = 1_3?
1st suggestion: Get rights to modify the db structure and figure out how to better store the Navision string.
2nd suggestion: CLR
I'll assume you are relatively comfortable with each of these concepts. If you aren't they are very well documented all over the web.
My approach would be to use a CLR function as there's going to be some high level things that are awkward in SQL that C# takes care of quite easily. The psuedo walk through would go something like this.
Implementation
Create a CLR funciton and implement it on the SQL server instance.
Using SQL resultset change the query to look for the returned value of the CLR function based on the navision filter value where "1_3".
CLR Function Logic
Create a c# function that takes in the value of the filter field and returns a string value.
The CLR function splits the filter field by the | char into a list.
Inside the CLR function create a second list. Iterate over the first list. When you find a ranged string split it on the ".." and manually add every available value between the range to the second list. When you find a value that isnt' ranged simply add it to the second list.
Join the contents of the second list together on the "|" charecter.
Return the joined value.
SQL Logic
SELECT Field1,Field2...CLRFunctionName(FilterValue) AS FixedFilterValue FROM Sometable WHERE FixedFilterValue LIKE '%1_3%';
I need to create functionality for users to determine the WHERE criteria of a select - the criteria will be dynamic.
Is there a way I can achieve this without opening up my code to SQL injection?
I'm using C# / .NET Windows Application.
Using parameterized queries would go long way toward protecting you from SQL injection attacks, because most bad things happen in the value portion of your where conditions.
For exampleg given a condition a=="hello" && b=="WORLD", do this:
select a,b,c,d
from table
where a=#pa and b=#pb -- this is generated dynamically
Then, bind #pa="hello" and #pb="WORLD", and run your query.
In C#, you would start with an in-memory representation of your where clause in hand, go through it element-by-element, and produce two output objects:
A string with the where clause, where constants are replaced by automatically generated parameter references pa, pb, and so on (use your favorite naming scheme for these blind parameters: the actual names do not matter)
A dictionary of name-value pairs, where names correspond to the parameters that you've inserted in your where clause, and values that correspond to the constants that you pulled from the expression representation.
With these outputs in hand, you prepare your dynamic query using the string, add parameter values using the dictionary, and then execute the query against your RDBMS source.
DO NOT DO THIS
select a,b,c,d
from table
where a='hello' and b='WORLD' -- This dynamic query is ripe for an interjection attack
Ah two phases. Given you column names and operators are not direct user input. E.g. picked from a list or radio group etc
then
String WhereClause = String.Format("Where {0} {1} #{0}","Customer", "=");
So now you Have "Where Customer = #Customer".
Then you can add aparamer Customer and set it from the user input.
There are a few ways to attack this, depends on how complex your criteria could be though.
I want to store an ID and a date and I want to retrieve all entries from dateA up to dateB, what exactly do I need to be able to perform select from my_column_family where date >= dateA and date < dateB; ?
the guys at #cassandra (IRC) helped me find a way, there's many subtle details so I'd like to document that here.
first you need to declare a column family similar to this (examples from cassandra-cli):
create column family users with comparator=UTF8Type and key_validation_class=UTF8Type and column_metadata=[
{column_name: id, validation_class: LongType}
{column_name: name, validation_class: UTF8Type, index_type: KEYS}
{column_name: age, validation_class: LongType}
];
few important things about this declaration:
the comparator and key_validation_class are there to be able to use strings as key names
the first declared column is special, it's the "row key" which is used to address each row and therefore cannot contain duplicate values (the INSERT is really an UPSERT so when there's duplicates the new values overwrite the old ones)
the second column declares a "secondary index" on its values (more on that below)
the dates are stored as Long datatypes, interpretation is up to the client
now let's add some values:
set users[1][name] = john;
set users[1][age] = 19;
set users[2][name] = jane;
set users[2][age] = 21;
set users[3][name] = john;
set users[3][age] = 32;
according to this: http://pkghosh.wordpress.com/2011/03/02/cassandra-secondary-index-patterns/ Cassandra does not support the < operators, what it does is to manually exclude the rows that don't match but it does that AFTER there's a resultset and it also refuses to do so unless and actual filtering has taken place.
what that means is that a query like get users where age > 20; will return null but if we add a predicate that includes = it'll magically work.
here's where the secondary index is important, without it you can't use = so on this example I can do get users where name = jane; but I cannot ask for get users where age = 21;
the funny thing is that, after using = the < works so having a secondary index allows you to ask for get users where name = john and age > 20; and it'll filter correctly.
There are a few ways to solve this. The simplest is probably the secondary index solution with the equality limitation mentioned in your own answer. I've used this method, adding an additional column called 'valid', setting the value to 1. Then the queries can become where valid=1 and date>nnnn
The other solutions require additional column families and additional queries.
When loading the data, create and add to a column family which contains the timestamps as keys, and each entry would list all the user ids as column names.
If the partitioning strategy is ordered, then a single RangeSliceQuery can specify the date range as a key range and get all the columns for each key. Then iterate through the result keys, using the column values for each user id and if needed, query the original column family for the data associated with each id. Cassandra always stores the column names sorted, and can be reversed when reading.
But, as documented, the ordered partitioner is not ideal, leading to hot spots and difficulty in load balancing the nodes.
Without the ordered partitioner, still keeping the timestamp column family, you would have to create another column family while loading data where you can store all the timestamps as the columns under one or more known keys (e.g. 'created' or 'updated'). The first query would be a SliceQuery for a known key, and then the column names (as timestamps) would provide the keys for the MultigetSliceQuery to the timestamp column family.
I've used variations on this, usually adding Composite keys or columns for additional flexibility.
In an XmlData column in SQL Server 2008 that has no schema assigned to it, how can I pull the first item at a particular node level? For example, I have:
SELECT
XmlData.value('//*/*[1]','NVARCHAR(6)')
FROM table
where XmlData.Exist('//*/*[1]') = 1
I assume this does not work because if there are multiple nodes with different names at the 2nd level, the first of each of those could be returned (and the value() requires that a singleton be selected.
Since I don't know what the names of any nodes will be, is there a way to always select whatever the first node is at the 2nd level?
I found the answer by chaining Xquery .query() and .value()
XMLDATA.query('//*/*[1]').value('.[1]','NVARCHAR(6)')
This returns the value of the first node and works perfectly for my needs.