I'm using https://github.com/stephencelis/SQLite.swift to implement SQLite in swift. I read through the documentation but couldn't find what's the return type for filter specifically here
https://github.com/stephencelis/SQLite.swift/blob/master/Documentation/Index.md#filtering-rows
The reason I'm asking is because I have a table called userTable containing all usernames, emails... of all users, but how can I lookup if a specific user exist?
For the filter function, I have no idea what Table.filter return type is if there is nothing found that's matching the condition.
Specifically if "bob01" is not in the table then what would
table.filter(username=="bob01")
return?
Thanks!
If you want to select data from table you can use "prepare" or "pluck" methods of library. When you write "table.filter(...)", you actually define a query. So you should give this query to one of the above functions.
Different of these functions are return type. "Prepare" returns an Array includes Row type and "Pluck" returns Row. And finally, Row is a class that comes with SQLite.swift library.
let query = table.filter(username=="bob01")
var row = try db!.pluck(query) //it's optional
There is a video about it but it's in Turkish language: https://www.youtube.com/watch?v=cXA6ehpli5I
Also there is a part of code on my github: https://github.com/sercan5534/swift-lesson/blob/master/Swift-DB-Operations/SQLiteTest/DBUtil.swift
Related
I have a Dataverse table named my_sample_table.
Inside the table I have a column named my_sample_column of type integer whose max value should be returned. Am trying to achieve this by using the List rows action provided with PowerAutomate.
Is there a filter query that can be written on the Filter rows property ? similar to what we use with SQL : max(columnname)
Or any other queries that can be included in the List rows action which will return the same result.
I know that I can iterate through the column values to get the max value using an expresion or by sorting it and getting the topmost one. But I was wondering whether there are any direct approach to it.
I would try and use a max aggregate for this column in a Fetch Xml query:
https://learn.microsoft.com/en-us/power-apps/developer/data-platform/use-fetchxml-aggregation#max
What I want
ores = {"Bauxite", "Coal", "Hematite"}
properties={["Bauxite"]={name="Bauxite", density=1.2808},["Coal"]={name="Coal" , density=1.3465},["Quartz"]={name="Quartz" , density=2.6498},["Hematite"]={name="Hematite" , density=5.0398}}
system.print(properties.ores[1].name)
system.print(properties.ores[1].density)
Should Output
Bauxite
1.2808
This is a recurrent question regarding indexing tables by a value rather than by a constant string. You're currently using ((properties.ores)[1]).name; this is not parsed as properties.(ores[1]).name as you seem to have expected. That's because . is always followed by an identifier - a constant string - which is used to index the table. table.key is just shorthand for table["key"] for keys matching [a-zA-Z_][a-zA-Z0-9_]*. If you want to dynamically index a table with some expression, you have to use table[expr].
To fix your code, simply do:
system.print(properties[ores[1]].name)
system.print(properties[ores[1]].density)
So, any reason behind happen this things, because when i perform sort() function with let type at that time xcode give me a compile time error
i tried it in my playgound with only sort function and sort() function with other higher order function.
like so
let name = ["mehul","HeLLi","JeniFER","Ankul"]
name.sort()
error :
Cannot use mutating member on immutable value: 'name' is a 'let' constant
but with other higher order functions
let nameStartingWithBArray = name.filter {$0.first != "B"}.map {$0.uppercased()}.sorted()
now there is no error
Please consider the subtle but crucial difference between sort and sorted
sort has no return value. It sorts in place that means the calling object is mutated.
sorted ( as well as filter and map) returns a new object with the result of the operation.
sort() basically works with the list itself. It modifies the original list in place. The return value is None.
name.sort() sorts the list and save the sorted list.
sorted() works on any iterable that may include list, dict and so on. It returns another list and doesn't modify the original list.
sorted() returns a sorted copy of the list (a new sorted list), without changing the original list.
Keynote : sort() is faster than sorted()
The sort function sorts the collection in place - i.e. it modifies the array, name, on which you call sort.
filter on the other hand returns an array and does not modify the original array.
Compare sort with sorted which again returns a new array and does not modify the original array.
So, you can write
let sortedNames = name.sorted()
sortedNames will be in order, while name will be in the original, unsorted, order.
If you write
var name = ["mehul","HeLLi","JeniFER","Ankul"]
name.sort()
then name will be in order, and because it is declared as var rather than a constant with let the change is permitted.
The sort func you are using is the mutating func, that means sort function internally sort the array in the same variable.
Mutating Func : To modify the properties of your structure or enumeration within a particular method, you can opt in to mutating behavior for that method. The method can then mutate (that is, change) its properties from within the method, and any changes that it makes are written back to the original structure when the method ends.
So. let doesn't allow sort for doing mutating, so you need to make it var.
More ever, if you use sorted(by:) , it returns new array of sorted values. So here you don't get any error.
I want to search by an attribute that contains an array. I'm interested in returning all records where the array in this attribute contains a specific value.
example object
Location_1 {
regions: ["on", "qc"]
}
I want to do something like this Location.where(regions: "on"), but I'm not sure of the correct syntax.
what is the right way to do this?
Try this Location.where('regions in (?)', ['on','qc'])
The IN operator allows you to specify multiple values in your WHERE clause.
Hopefully this is a little clearer. I'm sorry but I'm very new to coding in general. I have multiple tables that I have to query in succession in order to get to the correct array that I need. The following logic for the query is as follows:
this gives me an array based upon the store :id
store = Stores.find(params[:id])
this gives me another array based upon the param .location found in the table store where that value equals the row ID in the table Departments
department = Departments.find(store.location)
I need to preform one last query but in order to do so I need to figure out which day of the meeting is needed. In order to do this I have to create the parameter day_of_meeting found in the table Stores. I try to call it from the array above and create a new variable. In the Table Departments, I there are params such as day_1, day_2 and so on. I need to be able to call something like department.day_1 or department.day_2. Thus, I'm trying to actually create the variable by join the words "department.day_" to the variable store.day_of_meeting which would equal some integer, creating department.day_1...
which_day = ["department.day_", store.day_of_meeting].join("")
This query finds uses the value found from the variable department.day_1 to query table Meeting to find the values in the corresponding row.
meeting = Meeting.find(which_day)
Does this make my problem any clearer to understand?
findmethod can only accept parameters like Meeting.find(1) or Meeting.find("1-xx").
so, what you need is Meeting.find(department.send("day_" + store.day_of_meeting.to_s))
Hope to help!