Can someone please explain whats the difference between the two in Entity Framework.
Example1:
obj = new TicketsEntities();
var depts = obj.DEPARTMENTs.Select( x => x);
string str = depts.GetType().ToString();
In this case str prints --- System.Data.Entity.Infrastructure.DbQuery`1[LINQu.Models.DEPARTMENT]
Example2:
obj = new TicketsEntities();
var depts = obj.DEPARTMENTs;
string str = depts.GetType().ToString();
In this case str prints --- System.Data.Entity.DbSet`1[LINQu.Models.DEPARTMENT]
In either case when we loop through the depts we get same result , so what is the difference between the two , and which one is preferred ?
The DbSet represents the set of data and can manipulate the data by exposing methods like Add, Update, Remove.
The DbQuery represents a Linq query that is executed on a set of data. It does not have the Add, Update and Remove methods.
In your case I think there is no real difference, but for simplicity sake I would pick your second example since the Select(x=>x) is not neccessary.
Related
I am working with spring data jpa, I would like to know in QueryByExample(QBE) can i get all the records (where colum value not equals 'XXX')
I have seen ExampleMatcher , but couldnt find anything like not equals
Employee filterBy = new Employee();
filterBy.setLastName("ar");
//Filter - ignore case search and contains
ExampleMatcher matcher = ExampleMatcher.matching()
.withStringMatcher(StringMatcher.CONTAINING) // Match string containing pattern
.withIgnoreCase(); // ignore case sensitivity
example = Example.of(filterBy, matcher);
The above code gets all the records where lastname is ar, but i am looking for lastname should not be "ar".
Is there any other ExampleMatcher ?
BizExceptionConfig condition = configRequestPair.getCondition();
ExampleMatcher exampleMatcher = ExampleMatcher.matching()
.withMatcher("appCode", startsWith())
.withMatcher("name", startsWith())
.withMatcher("code", startsWith());
if(Objects.isNull(condition.getLifecycle())){
condition.setLifecycle(LifeCycle.DELETE.getCode());
HashMap<String, Integer> params = new HashMap<>();
params.put("$ne", LifeCycle.DELETE.getCode());
exampleMatcher = exampleMatcher.withTransformer("lifecycle", (obj) -> Optional.of(params));
}
Example<BizExceptionConfig> example = Example.of(condition, exampleMatcher);
Page<BizExceptionConfig> pageRecord = bizExcConfigRepository.findAll(example, PageUtil.toPageRequest(configRequestPair.getPage()));`enter code here`
This problem can be solved by "withTransformer". JPA is rather limited,
so I suggest using Mongotmpl. I hope it can help you
Your problem could be solved with QBE by using REGEX as StringMatcher and the solution would look like the following:
Employee filterBy = new Employee();
filterBy.setLastName("ar");
filterBy.setLastName(String.format("^(?!.*$1$).*$", Pattern.quote(filterBy.getLastName())));
//filterBy.setLastName(String.format(".*(?<!$1)$", Pattern.quote(filterBy.getLastName()))); // this would be another alternative
ExampleMatcher matcher = ExampleMatcher.matching()
.withStringMatcher(StringMatcher.REGEX) // Match string containing pattern
.withIgnoreCase(); // ignore case sensitivity
Example example = Example.of(filterBy, matcher);
Unfortunately, even though the developer would at first think that Regular Expressions are supported (as there exists aforementioned enum constant), Spring actually currently doesn't support them - and according to the discussion of the related Jira issue, it never won't: https://jira.spring.io/browse/DATAJPA-944
My Linq Query keeps returning the null error on FirstOrDefault
The cast to value type 'System.Int32' failed because the materialized value is null
because it can't find any records to match on the ClinicalAssetID form the ClinicalReading Table, fair enough!
But I want the fields in my details page just to appear blank if the table does not have matching entry.
But how can I handle the null issue when using the order by function ?
Current Code:
var ClinicalASSPATINCVM = (from s in db.ClinicalAssets
join cp in db.ClinicalPATs on s.ClinicalAssetID equals cp.ClinicalAssetID into AP
from subASSPAT in AP.DefaultIfEmpty()
join ci in db.ClinicalINSs on s.ClinicalAssetID equals ci.ClinicalAssetID into AI
from subASSINC in AI.DefaultIfEmpty()
join co in db.ClinicalReadings on s.ClinicalAssetID equals co.ClinicalAssetID into AR
let subASSRED = AR.OrderByDescending(subASSRED => subASSRED.MeterReadingDone).FirstOrDefault()
select new ClinicalASSPATINCVM
{
ClinicalAssetID = s.ClinicalAssetID,
AssetTypeName = s.AssetTypeName,
ProductName = s.ProductName,
ModelName = s.ModelName,
SupplierName = s.SupplierName,
ManufacturerName = s.ManufacturerName,
SerialNo = s.SerialNo,
PurchaseDate = s.PurchaseDate,
PoNo = s.PoNo,
Costing = s.Costing,
TeamName = s.TeamName,
StaffName = s.StaffName,
WarrantyEndDate = subASSPAT.WarrantyEndDate,
InspectionDate = subASSPAT.InspectionDate,
InspectionOutcomeResult = subASSPAT.InspectionOutcomeResult,
InspectionDocumnets = subASSPAT.InspectionDocumnets,
LastTypeofInspection = subASSINC.LastTypeofInspection,
NextInspectionDate = subASSINC.NextInspectionDate,
NextInspectionType = subASSINC.NextInspectionType,
MeterReadingDone = subASSRED.MeterReadingDone,
MeterReadingDue = subASSRED.MeterReadingDue,
MeterReading = subASSRED.MeterReading,
MeterUnitsUsed = subASSRED.MeterUnitsUsed,
FilterReplaced = subASSRED.FilterReplaced
}).FirstOrDefault(x => x.ClinicalAssetID == id);
Tried this but doesn't work
.DefaultIfEmpty(new ClinicalASSPATINCVM())
.FirstOrDefault()
Error was:
CS1929 'IOrderedEnumerable<ClinicalReading>' does not contain a definition for 'DefaultIfEmpty' and the best extension method overload 'Queryable.DefaultIfEmpty<ClinicalASSPATINCVM>(IQueryable<ClinicalASSPATINCVM>, ClinicalASSPATINCVM)' requires a receiver of type 'IQueryable<ClinicalASSPATINCVM>'
Feel a little closer with this but still errors
let subASSRED = AR.OrderByDescending(subASSRED => (subASSRED.MeterReadingDone != null) ? subASSRED.MeterReadingDone : String.Empty).FirstOrDefault()
Error:
CS0173 Type of conditional expression cannot be determined because there is no implicit conversion between 'System.DateTime?' and 'string'
The original error means that some of the following properties of the ClinicalASSPATINCVM class - MeterReadingDone, MeterReadingDue, MeterReading, MeterUnitsUsed, or FilterReplaced is of type int.
Remember that subASSRED here
let subASSRED = AR.OrderByDescending(subASSRED => subASSRED.MeterReadingDone).FirstOrDefault()
might be null (no corresponding record).
Now look at this part of the projection:
MeterReadingDone = subASSRED.MeterReadingDone,
MeterReadingDue = subASSRED.MeterReadingDue,
MeterReading = subASSRED.MeterReading,
MeterUnitsUsed = subASSRED.MeterUnitsUsed,
FilterReplaced = subASSRED.FilterReplaced
If that was LINQ to Objects, all these would generate NRE (Null Reference Exception) at runtime. In LINQ to Entities this is converted and executed as SQL. SQL has no issues with expression like subASSRED.SomeProperty because SQL supports NULL naturally even if SomeProperty normally does not allow NULL. So the SQL query executes normally, but now EF must materialize the result into objects, and the C# object property is not nullable, hence the error in question.
To solve it, find the int property(es) and use the following pattern inside query:
SomeIntProperty = (int?)subASSRED.SomeIntProperty ?? 0 // or other meaningful default
or change receiving object property type to int? and leave the original query as is.
Do the same for any non nullable type property, e.g. DateTime, double, decimal, Guid etc.
You're problem is because your DefaultIfEmpty is executed AsQueryable. Perform it AsEnumerable and it will work:
// create the default element only once!
static readonly ClinicalAssPatInVcm defaultElement = new ClinicalAssPatInVcm ();
var result = <my big linq query>
.Where(x => x.ClinicalAssetID == id)
.AsEnumerable()
.DefaultIfEmpty(defaultElement)
.FirstOrDefault();
This won't lead to a performance penalty!
Database management systems are extremely optimized for selecting data. One of the slower parts of a database query is the transport of the selected data to your local process. Hence it is wise to let the DBMS do most of the selecting, and only after you know that you only have the data that you really plan to use, move the data to your local process.
In your case, you need at utmost one element from your DBMS, and if there is nothing, you want to use a default object instead.
AsQueryable will move the selected data to your local process in a smart way, probably per "page" of selected data.
The page size is a good compromise: not too small, so you don't have to ask for the next page too often; not too large, so that you don't transfer much more items than you actually use.
Besides, because of the Where statement you expect at utmost one element anyway. So that a full "page" is fetched is no problem, the page will contain only one element.
After the page is fetched, DefaultIfEmpty checks if the page is empty, and if so, returns a sequence containing the defaultElement. If not, it returns the complete page.
After the DefaultIfEmpty you only take the first element, which is what you want.
Since the documentation and tutorials on collections in Ponylang are lacking, I'm really struggling in using the Array class and working with indices.
I have an overenginered actor-based fizzbuzz where there's an actor in charge of requesting fizzbuzz operations to other actors and collecting the results. Probably the pattern I'm using is not the best but right now I would like to iterate in this way to learn more.
My problem is with the following code:
actor FizzBuzzer
var _results:Array[String]
let _main: Main tag
fun list_to_string(l:List[String]):String=>
l.fold[String]({(a:String,b:String)=>a+"\n"+b},"")
new create(n:String, main:Main tag)=>
let num:USize = try (consume n).usize()? else 0 end
_main = main
_results = recover Array[String] end
try
let result = this.fizzbuzz(num)?
let message:String = list_to_string(result)
main.print(message)
else
main.print("Invalid argument: "+ num.string())
end
fun fizzbuzz(n:USize, acc:List[String]=List[String]()):List[String] ?=>
if n <=0 then error end
let res = List[String]()
for i in Range[USize](1,n+1) do
FizzBuzzerino.process(i,this)
end
res
be collect_result(result:String,num:USize)=>
try
_results.insert(num,result)?
else
_main.print("Error processing element: "+num.string())
end
`
In the function collect_result the insertion always fails. Using update is the same. The result and num I receive from the processing actor are correct but I cannot insert them in the array. Any insertion in the Array in this class fails. Is it a matter of capabilities? Or am I doing something wrong?
i am trying to make a game where players create their own buildings and can then save them for other players to see and play on. However, roblox doesn't let me store all the data needed for the whole creation(there are several properties for each brick)
All i get is this error code:
104: Cannot store Array in DataStore
any help would be greatly appreciated!
I'm not sure if this is the best method, but it's my attempt. Below is an example of a table, you can use tables to store several values. I think you can use HttpService's JSONEncode function to convert tables into strings (which hopefully can be saved more efficiently)
JSONEncode (putting brick's data into a string, which you can save into the DataStore
local HttpService = game:GetService("HttpService")
-- this is an example of what we'll convert into a json string
local exampleBrick = {
["Size"] = Vector3.new(3,3,3),
["Position"] = Vector3.new(0,1.5,0),
["BrickColor"] = BrickColor.new("White")
["Material"] = "Concrete"
}
local brickJSON = HttpService:JSONEncode(exampleBrick)
print(brickJSON)
-- when printed, you'll get something like
-- { "Size": Vector3.new(3,3,3), "Position": Vector3.new(0,1.5,0), "BrickColor": BrickColor.new("White"), "Material": "Concrete"}
-- if you want to refer to this string in a script, surround it with two square brackets ([[) e.g. [[{"Size": Vector3.new(3,3,3)... }]]
JSONDecode (reading the string and converting it back into a brick)
local HttpService = game:GetService("HttpService")
local brickJSON = [[ {"Size": Vector3.new(3,3,3), "Position": Vector3.new(0,1.5,0), "BrickColor": BrickColor.new("White"), "Material": "Concrete"} ]]
function createBrick(tab)
local brick = Instance.new("Part")
brick.Parent = <insert parent here>
brick.Size = tab[1]
brick.Position= tab[2]
brick.BrickColor= tab[3]
brick.Material= tab[4]
end
local brickData = HttpService:JSONDecode(brickJSON)
createBrick(brickData) --this line actually spawns the brick
The function can also be wrapped in a pcall if you want to account for any possible datastore errors.
Encoding a whole model into a string
Say your player's 'building' is a model, you can use the above encode script to convert all parts inside a model into a json string to save.
local HttpService = game:GetService("HttpService")
local StuffWeWantToSave = {}
function getPartData(part)
return( {part.Size,part.Position,part.BrickColor,part.Material} )
end
local model = workspace.Building --change this to what the model is
local modelTable = model:Descendants()
for i,v in pairs(modelTable) do
if v:IsA("Part") or v:IsA("WedgePart") then
table.insert(StuffWeWantToSave, HttpService:JSONEncode(getPartData(modelTable[v])))
end
end
Decoding a string into a whole model
This will probably occur when the server is loading a player's data.
local HttpService = game:GetService("HttpService")
local SavedStuff = game:GetService("DataStoreService"):GetDataStore("blabla") --I don't know how you save your data, so you'll need to adjust this and the rest of the scripts (as long as you've saved the string somewhere in the player's DataStore)
function createBrick(tab)
local brick = Instance.new("Part")
brick.Parent = <insert parent here>
brick.Size = tab[1]
brick.Position= tab[2]
brick.BrickColor= tab[3]
brick.Material= tab[4]
end
local model = Instance.new("Model") --if you already have 'bases' for the players to load their stuff in, remove this instance.new
model.Parent = workspace
for i,v in pairs(SavedStuff) do
if v[1] ~= nil then
CreateBrick(v)
end
end
FilteringEnabled
If your game uses filteringenabled, make sure that only the server handles saving and loading data!! (you probably already knew that) If you want the player to save by clicking a gui button, make the gui button fire a RemoteFunction that sends their base's data to the server to convert it to a string.
BTW I'm not that good at scripting so I've probably made a mistake somehwere.. good luck though
Crabway's answer is correct in that the HttpService's JSONEncode and JSONDecode methods are the way to go about tackling this problem. As it says on the developer reference page for the DataStoreService, Data is ... saved as a string in data stores, regardless of its initial type. (https://developer.roblox.com/articles/Datastore-Errors.) This explains the error you received, as you cannot simply push a table to the data store; instead, you must first encode a table's data into a string using JSONEncode.
While I agree with much of Crabway's answer, I believe the function createBrick would not behave as intended. Consider the following trivial example:
httpService = game:GetService("HttpService")
t = {
hello = 1,
goodbye = 2
}
s = httpService:JSONEncode(t)
print(s)
> {"goodbye":2,"hello":1}
u = httpService:JSONDecode(s)
for k, v in pairs(u) do print(k, v) end
> hello 1
> goodbye 2
As you can see, the table returned by JSONDecode, like the original, uses strings as keys rather than numeric indices. Therefore, createBrick should be written something like this:
function createBrick(t)
local brick = Instance.new("Part")
brick.Size = t.Size
brick.Position = t.Position
brick.BrickColor = t.BrickColor
brick.Material = t.Material
-- FIXME: set any other necessary properties.
-- NOTE: try to set parent last for optimization reasons.
brick.Parent = t.Parent
return brick
end
As for encoding a model, calling GetChildren would produce a table of the model's children, which you could then loop through and encode the properties of everything within. Note that in Crabway's answer, he only accounts for Parts and WedgeParts. You should account for all parts using object:IsA("BasePart") and also check for unions with object:IsA("UnionOperation"). The following is a very basic example in which I do not store the encoded data; rather, I am just trying to show how to check the necessary cases.
function encodeModel(model)
local children = model:GetChildren()
for _, child in ipairs(children) do
if ((child:IsA("BasePart")) or (child:IsA("UnionOperation"))) then
-- FIXME: encode child
else if (child:IsA("Model")) then
-- FIXME: using recursion, loop through the sub-model's children.
end
end
return
end
For userdata, such as Vector3s or BrickColors, you will probably want to convert those to strings when you go to encode them with JSONEncode.
-- Example: part with "Brick red" BrickColor.
color = tostring(part.BrickColor)
print(string.format("%q", color))
> "Bright red"
I suggest what #Crabway said, use HttpService.
local httpService = game:GetService("HttpService")
print(httpService:JSONEncode({a = "b", b = "c"}) -- {"a":"b","b":"c"}
But if you have any UserData values such as Vector3s, CFrames, Color3s, BrickColors and Enum items, then use this library by Defaultio. It's actually pretty nice.
local library = require(workspace:WaitForChild("JSONWithUserdata"))
library:Encode({Vector3.new(0, 0, 0)})
If you want a little documentation, then look at the first comment in the script:
-- Defaultio
--[[
This module adds support for encoding userdata values to JSON strings.
It also supports lists which skip indices, such as {[1] = "a", [2] = "b", [4] = "c"}
Userdata support is implemented by replacing userdata types with a new table, with keys _T and _V:
_T = userdata type enum (index in the supportedUserdataTypes list)
_V = a value or table representing the value
Follow the examples bellow to add suppport for additional userdata types.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Usage example:
local myTable = {CFrame.new(), BrickColor.Random(), 4, "String", Enum.Material.CorrodedMetal}
local jsonModule = require(PATH_TO_MODULE)
local jsonString = jsonModule:Encode(myTable)
local decodedTable = jsonModule:Decode(jsonString)
--]]
I have standard list of objects which is used for the some analysis. The analysis generates a list of Strings and i need to look through the standard list of objects and retrieve objects with same name.
case class TestObj(name:String,positions:List[Int],present:Boolean)
val stdLis:List[TestObj]
//analysis generates a list of strings
var generatedLis:List[String]
//list to save objects found in standard list
val lisBuf = new ListBuffer[TestObj]()
//my current way
generatedLis.foreach{i=>
val temp = stdLis.filter(p=>p.name.equalsIgnoreCase(i))
if(temp.size==1){
lisBuf.append(temp(0))
}
}
Is there any other way to achieve this. Like having an custom indexof method that over rides and looks for the name instead of the whole object or something. I have not tried that approach as i am not sure about it.
stdLis.filter(testObj => generatedLis.exists(_.equalsIgnoreCase(testObj.name)))
use filter to filter elements from 'stdLis' per predicate
use exists to check if 'generatedLis' has a value of ....
Don't use mutable containers to filter sequences.
Naive solution:
val lisBuf =
for {
str <- generatedLis
temp = stdLis.filter(_.name.equalsIgnoreCase(str))
if temp.size == 1
} yield temp(0)
if we discard condition temp.size == 1 (i'm not sure it is legal or not):
val lisBuf = stdLis.filter(s => generatedLis.exists(_.equalsIgnoreCase(s.name)))