I am using exposed in one project, and I have a table lets call it TableX with two properties
property1 and x knowing that x is nullable
I added TableX.x.isNotNull() to my query so I can ignore null rows!.
And I have Object1 with also two properties as TableX which are: property1 and x knowing that x is not null in Object1
Then when I create Object1 out of the rows from the query, the compiler will nag about x because it should not be null and we are receiving a nullable x from TableX.
So I have added !! when setting x in Object1, given that I am sure that the query will never return any row with x is null because of the constraint that I have added.
But still, I receive KotlinNullPointerException some times. So how is this possible?
I thought of some compatibility issues between MySQL and exposed! But couldn't find any
val result = listOf<Object1>()
transaction {
val query = TableX.select {
TableX.property1.eq(123) and
TableX.x.isNotNull()
}
.fetchSize(1000)
result = query.map {
Object1(
property1 = it[TableX.property1],
x = it[TableX.x]!!
)
}
}
I'm facing the same problem in a company I am working now. And it looks like you have race condition in place. Try to explicitly check for null before building result list. At least you won't get an exception.
Related
i want to count the data type of each redis key, I write following code, but run error, how to fix it?
local detail = {}
detail.hash = 0
detail.set = 0
detail.string = 0
local match = redis.call('KEYS','*')
for i,v in ipairs(match) do
local val = redis.call('TYPE',v)
detail.val = detail.val + 1
end
return detail
(error) ERR Error running script (call to f_29ae9e57b4b82e2ae1d5020e418f04fcc98ebef4): #user_script:10: user_script:10: attempt to perform arithmetic on field 'val' (a nil value)
The error tells you that detail.val is nil. That means that there is no table value for key "val". Hence you are not allowed to do any arithmetic operations on it.
Problem a)
detail.val is syntactic sugar for detail["val"]. So if you expect val to be a string the correct way to use it as a table key is detail[val].
Possible problem b)
Doing a quick research I found that this redis call might return a table, not a string. So if detail[val] doesn't work check val's type.
I am making quite the complex thing and I am trying to use tables as variable names cause I have found that lua works with it, that is:
lua
{[{1,2}]="Meep"}
The issue is it is callable, when I do it and try to call it using the same kind of table, it won't find it.
I have tried looking for it and such but I have no clue why it won't do this.
ua
local c = {[{1,2}]="Meep"}
print(c[{1,2}],c)
Do I expect to become but it does not.
"Meep",{[{1,2}]="Meep"}
but what I get is
nil,{[{1,2}]="Meep"}
If I however try
lua
local m={1,2}
local c = {[m]="Meep"}
print(c[m],c)
it becomes the correct one, is there a way to avoid that middle man? After all m=={1,2} will return true.
The problem you have is that tables in lua are represented as references. If you compare two different talbes you are comparing those references. So the equation only gets true if the given tables are exactly the same.
t = { 1, 2, 3 }
t2 = { 1, 2, 3 }
print(t == t) -- true
print(t2 == t) -- false
print(t2 == t2) -- true
Because of this fact, you can pass them in function per reference.
function f(t)
t[1] = 5
end
t2 = { 1 }
f(t2)
print(t2[1]) -- 5
To bypass this behavior, you could (like suggested in comments) serialize the table before using it as a key.
My problem is simple.
I have a column seqNum: Double which is NOT NULL DEFAULT 1 in CREATE TABLE statement as follows:
CREATE TABLE some_table
(
...
seq_num DECIMAL(18,10) NOT NULL DEFAULT 1,
...
);
User can enter a value for seqNum or not from UI. So the accepting PLAY form is like:
case class SomeCaseClass(..., seqNum: Option[Double], ...)
val secForm = Form(mapping(
...
"seqNum" -> optional(of[Double]),
...
)(SomeCaseClass.apply)(SomeCaseClass.unapply))
The slick Table Schema & Objects looks like this:
case class SomeSection (
...
seqNum: Option[Double],
...
)
class SomeSections(tag: Tag) extends Table[SomeSection](tag, "some_table") {
def * = (
...
seqNum.?,
...
) <> (SomeSection.tupled, SomeSection.unapply _)
...
def seqNum = column[Double]("seq_num", O.NotNull, O.Default(1))
...
}
object SomeSections {
val someSections = TableQuery[SomeSections]
val autoInc = someSections returning someSections.map(_.sectionId)
def insert(s: someSection)(implicit session: Session) = {
autoInc.insert(s)
}
}
When I'm sending seqNum from UI, everything is works fine but when None is there, it breaks saying that cannot insert NULL in NOT NULL column which is correct. This question explains why.
But how to solve this problem using slick? Can't understand where should I check about None? I'm creating & sending an object of SomeSection to insert method of SomeSections Object.
I'm using sql-server, if it matters.
Using the default requires not inserting the value at all rather than inserting NULL. This means you will need a custom projection to insert to.
people.map(_.name).insert("Chris") will use defaults for all other fields. The limitations of scala's native tuple transformations and case class transformations can make this a bit of a hassle. Things like Slick's HLists, Shapeless, Scala Records or Scala XR can help, but are not trivial or very experimental at the moment.
Either you enforce the Option passed to Slick by suffixing it with a .getOrElse(theDefault), or you make the DB accepts NULL (from a None value) and defaults it using some trigger.
I would like to use a Groovy closure to process data coming from a SQL table. For each new row, the computation would depend on what has been computed previously. However, new rows may become available on further runs of the application, so I would like to be able to reload the closure, initialised with the intermediate state it had when the closure was last executed in the previous run of the application.
For example, a closure intending to compute the moving average over 3 rows would be implemented like this:
def prev2Val = null
def prevVal = null
def prevId = null
Closure c = { row ->
println([ prev2Val, prevVal, prevId])
def latestVal = row['val']
if (prev2Val != null) {
def movMean = (prev2Val + prevVal + latestVal) / 3
sql.execute("INSERT INTO output(id, val) VALUES (?, ?)", [prevId, movMean])
}
sql.execute("UPDATE test_data SET processed=TRUE WHERE id=?", [row['id']])
prev2Val = prevVal
prevVal = latestVal
prevId = row['id']
}
test_data has 3 columns: id (auto-incremented primary key), value and processed. A moving mean is calculated based on the two previous values and inserted into the output table, against the id of the previous row. Processed rows are flagged with processed=TRUE.
If all the data was available from the start, this could be called like this:
sql.eachRow("SELECT id, val FROM test_data WHERE processed=FALSE ORDER BY id", c)
The problem comes when new rows become available after the application has already been run. This can be simulated by processing a small batch each time (e.g. using LIMIT 5 in the previous statement).
I would like to be able to dump the full state of the closure at the end of the execution of eachRow (saving the intermediate data somewhere in the database for example) and re-initialise it again when I re-run the whole application (by loading those intermediate variable from the database).
In this particular example, I can do this manually by storing the values of prev2Val, prevVal and prevId, but I'm looking for a generic solution where knowing exactly which variables are used wouldn't be necessary.
Perhaps something like c.getState() which would return [ prev2Val: 1, prevVal: 2, prevId: 6] (for example), and where I could use c.setState([ prev2Val: 1, prevVal: 2, prevId: 6]) next time the application is executed (if there is a state stored).
I would also need to exclude sql from the list. It seems this can be done using c.#sql=null.
I realise this is unlikely to work in the general case, but I'm looking for something sufficiently generic for most cases. I've tried to dehydrate, serialize and rehydrate the closure, as described in this Groovy issue, but I'm not sure how to save and store all the # fields in a single operation.
Is this possible? Is there a better way to remember state between executions, assuming the list of variables used by the closure isn't necessarily known in advance?
Not sure this will work in the long run, and you might be better returning a list containing the values to pass to the closure to get the next set of data, but you can interrogate the binding of the closure.
Given:
def closure = { row ->
a = 1
b = 2
c = 4
}
If you execute it:
closure( 1 )
You can then compose a function like:
def extractVarsFromClosure( Closure cl ) {
cl.binding.variables.findAll {
!it.key.startsWith( '_' ) && it.key != 'args'
}
}
Which when executed:
println extractVarsFromClosure( closure )
prints:
['a':1, 'b':2, 'c':4]
However, any 'free' variables defined in the local binding (without a def) will be in the closures binding too, so:
fish = 42
println extractVarsFromClosure( closure )
will print:
['a':1, 'b':2, 'c':4, 'fish':42]
But
def fish = 42
println extractVarsFromClosure( closure )
will not print the value fish
I'm trying to create an SQL query in PHP to update a table.
Is it possible to have a different WHERE clause for each affected row?
eg something like:
UPDATE table
SET val=X WHERE someproperty = 1,
SET val=Y WHERE someproperty = 2
etc?
Any help appreciated. Thanks
Yes, you can with a CASE statement.
UPDATE table
SET val = CASE someproperty
WHEN 1 THEN x
WHEN 2 THEN y
....
ELSE
val
END
Now, there is concern that one CASE statement is less readable when compared to several UPDATE statements. There is a valid argument here. For example, when 1000 rows are being updated, it just feels and looks better to use several UPDATE statements rather than 1000 different conditions to a single CASE.
However, sometimes a CASE statement is more appropriate. If, for example, you are updating rows based on some trait, say the even or odd nature of a field's value the table, then a CASE statement is a wonderfully concise and maintainable way to update rows in the table without having to resort to a huge number of UPDATE statements that all share a specific type of logic. Take this for example:
UPDATE table
SET val = CASE MOD(someproperty, 2)
WHEN 0 THEN x
WHEN 1 THEN y
END
This expression takes the modulus of someproperty and, when 0 (even), assigns value x to val and, when 1 (odd), assigns value y to val. The greater the volume of data being updated by this statement, the cleaner it is compared to doing so by multiple UPDATE statements.
In short, CASE statements are sometimes just as readable/maintainable as UPDATE statements. It all depends on what you are trying to do with them.
EDIT: Added the ELSE clause to be extra safe. The OP may be interested in updating only specific rows so the rest should remain as they prior to the UPDATE.
EDIT: Added a scenario where the CASE statement is a more effective approach than multiple UPDATE statements.
You cannot have multiple WHERE clauses for any SQL statement, however you can use a CASE statement to accomplish what you are trying to do. Another option that you have is to execute multiple UPDATE statements.
Here is a sample using the CASE statement:
UPDATE table
SET val = (
CASE someproperty
WHEN 1 THEN X
WHEN 2 THEN Y
ELSE val
END
);
Here is a sample using multiple UPDATE statements:
UPDATE table SET val=X WHERE someproperty = 1;
UPDATE table SET val=Y WHERE someproperty = 2;
Nope. Make it two updates:
UPDATE table SET val=X WHERE someproperty = 1;
UPDATE table SET val=Y WHERE someproperty = 2;
On second thought, you could use sub-queries or the case statement...
UPDATE table SET val= ( case when someproperty = 1 then X when someproperty = 2 then Y else val END )
You may need to make that a sub query like this:
UPDATE table t1 SET val = ( select CASE when someproperty = 1 then X when someproperty = 2 then Y ELSE val END from table t2 where t1.primarykey = t2.primary key )
UPDATE TABLE
SET VAL CASE SOMEPROPERTY WHEN 1 THEN X WHEN 2 THEN Y END
A compact and easily scaleable way:
UPDATE table1 SET val=ELT(FIND_IN_SET(someproperty, '1, 2'), X, Y);
make the query this way:
$condition = array(1, 2);
$newvals = array('X', 'Y');
$query = "UPDATE table1 SET val=ELT(FIND_IN_SET(someproperty, '". implode(',', $condition). "', ". implode(', ', $newvals). ")";
Use prepare_query to avoid SQL syntax errors if you deal with string values.