Im new to linQ and I've got a problem
Question: if i have a string Example "MySTring"and I need the characters at positions 5 and 6 counting from the right of the string, ie: "ST"
here's my Query
Dim result = From everyval in AllVals
where everyval.Substring(5,2)='ST'
select everyval.Name
Now this wont return the correct values from the database because the default Consideration of positions in the Substring Function is from LEft to Right.
One Solution is maybe to reverse the String and then apply the Substring Function to it.
But how should i be doing this?
can someone tell me..???
This is a rather strange requirement, usually an IndexOf/Contains is good enough for this. However, you could try (conceptually) truncating the value and testing the end using EndsWith.
Something like this perhaps (untested and probably doesn't work):
Dim result = from everyval in AllVals where everyval.Remove(4).EndsWidth("ST")
MSDN nicely lists the string functions that can be safely translated to SQL from LINQ: http://msdn.microsoft.com/en-us/vbasic/bb688085
Related
So, I am trying to execute a query using ArcGIS API, but it should match any Json queries. I am kind of new to this query format, so I am pretty sure I must be missing something, but I can't figure out what it is.
This page allows for testing queries on the database before I actually implement them in my code. Features in this database have several fields, including OBJECTID and Identificatie. I would like to, for example, select the feature where Identificatie = 1. If I enter this in the Where field though (Identificatie = 1) an error Failed to execute appears. This happens for every field, except for OBJECTID. Querying where OBJECTID = 1 returns the correct results. I am obviously doing something wrong, but I don't get it why OBJECTID does work here. A brief explanation (or a link to a page documenting queries for JSON, which I haven't found), would be appreciated!
Identificatie, along with most other fields in the service you're using, is a string field. Therefore, you need to use single quotes in your WHERE clause:
Identificatie = '1'
Or to get one that actually exists:
Identificatie = '1714100000729432'
OBJECTID = 1 works without quotes because it's a numeric field.
Here's a link to the correct query. And here's a link to the query with all output fields included.
I am using lua script
https://github.com/clofresh/mysql-proxy-cache to cache the select query.
But there is a problem with the way it is detecting select statement.
It is using following code
return query:sub(1,6):lower() == 'select'
This will not work if select query is nested in (). Example:
(SELECT * from tbl_name);
Is there a way to remove extra () in mysql proxy ?
or Is there a better way to detect select query?
I would try to write a normalizing script using the String Library that detect common patterns and replaces them with equivalent normalized sql.
One example is your parenteses but also queries where the where parts have been moved around could benefit from this.
The queries are actually inside of the the parentheses, not inside of a string? That shouldn't parse correctly, even with a plug in. If it is in a string then simply use :sub(2, 7), however, if it is not, then put it inside of a string. Create a function that basically reproduces the function, except puts it in a string, e.g.:
function mysqlQuery(mysqlString)
loadstring(mysqlString)();
return mysqlString;
end
mysqlQuery("SELECT * from tbl");
I am using DBIx::Class and I would like to select rows based on what day of the year they were inserted on. Below is my query:
$rows = $c->model("DB::Test")->search(
{
"DAYOFYEAR(entry_time)"=>$day_of_year,
});
However this doesn't work because DBIx::Class treats DAYOFYEAR(entry_time) as a column. Is there anyway I could have it use that value litteraly? I know sometimes making it a scalar such as \'DAYOFYEAR(entry_time)' will work for some situations, but I've tried that and it doesn't work. Does anyone know of a way that I could do this? Thanks!
Using \ and 'DAYOFYEAR(entry_time)' is the right approach, and part of the FAQ.
[How do I] .. search with an SQL function on the left hand side?
To use an SQL function on the left hand side of a comparison you currently need to resort to literal SQL:
->search( \[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ] );
Note: the plain_value string in the [ plain_value => 1979 ] part should be either the same as the name of the column (do this if the type of the return value of the function is the same as the type of the column) or in the case of a function it's currently treated as a dummy string (it is a good idea to use plain_value or something similar to convey intent). The value is currently only significant when handling special column types (BLOBs, arrays, etc.), but this may change in the future.
I have a big ResultSet (getting from a JDBC query) of few thousand rows. Using each of these rows, I have to instantiate an Object, setting fields of it according to the fields of this result set. Now, as we all know, the getXXX() methods of this JDBC API return 0 if that particular column was null. So for each field of each row, I have to do a wasNull() before setting the value in my object, which looks pretty ugly and may be is not efficient as well. So, is there any other way by which I can avoid it?
Apart from JDBC, if there is some entirely different, standard, commonly used way, I am open to know about that as well.
Thanks!
EDIT 1
patientInput.setRaceCodeId(patients.getShort("race_code_id"));
if(patients.wasNull())
patientInput.setRaceCodeId(null);
patients is a ResultSet. patientInput is an object. This is the code which I am trying to avoid. I mean, everytime I do a getXXX(), and do a setXXX(), I have to check again that what I got from ResultSet was not null. If it was, then set that object field as null, as getXXX() returns 0 in that case.
Ok. I believe there are two possible approaches to 'tidying' up your code. However, this could come down to a difference of opinion as to what is tidy!
Solution 1 - replace getXXX() with getObject() which returns null e.g.
Short s = (Short)patients.getObject("race_code_id");
patientInput.setRaceCodeId(s);
Solution 2 - write a generic wrapper method that retrieves nullable values
protected final <T> T getNullableValue(T returnType, String colName, ResultSet rs) throws SQLException {
Object colValue = rs.getObject(colName);
return (T) colValue;
}
final static Integer INT = 0;
final static Short SHORT = 0;
.
.
.
patientInput.setRaceCodeId(getNullableValue(SHORT,"race_code_id",patients));
You don't have to do it to each field, only to fields that are numeric and, possibly, boolean, and are declared as nullable in your database. It happens not as frequently as you fear.
If you absolutely hate writing such code, you can try switching to an ORM library, for example, Hibernate.
I ran into an issue where I need to call a UDF within my LINQ to SQL and then another stored procedure within that. Here's the code.
public IQueryable<DataDTO> GetLotsaData(string dataId, DateTime date, string custIDs)
{
var data = (from rs in _context.spXI_GetData(dataId, date, custIDs)
select new DataDTO
{
Time = rs.Time,
TimeZone = _context.GetTimezone(postDate, _context.GetDetailedData(rs.PKID, custIDs).FirstOrDefault().Zip),
CompletedTime = rs.Completed_Time,
});
return data.AsQueryable<DataDTO>();
}
The line I'm worried about is the one where I'm calling the GetTimezone UDF. Is it inefficient to call a UDF in the middle of a LINQ query and then another stored procedure (GetDetailedData) to get a single value for that UDF? What kind of SQL would this generate?
It looks a bit convoluted to me, but still better than the alternative which would be a sub-select or join in my stored procedure. (I'm trying to avoid having my stored procedure return the new field - TimeZone - instead just having it returned in my DTO.) And yes, I realize this could all be avoided if we were using UTC. Sadly, I have no control over that.
Why can't spXI_GetData return the complete result set? I'd say that would be optimal in this situation.
The GetTimezone and GetDetailedData functions will be called for every row in the spXI_GetData set. Would be better if the GetTimezone function could return a inline table and than you could join with it instead.