How can I store an array of doubles to database using Entity Framework Code-First with no impact on the existing code and architecture design?
I've looked at Data Annotation and Fluent API, I've also considered converting the double array to a string of bytes and store that byte to the database in it own column.
I cannot access the public double[] Data { get; set; } property with Fluent API, the error message I then get is:
The type double[] must be a non-nullable value type in order to use
it as parameter 'T'.
The class where Data is stored is successfully stored in the database, and the relationships to this class. I'm only missing the Data column.
You can do a thing like this :
[NotMapped]
public double[] Data
{
get
{
string[] tab = this.InternalData.Split(',');
return new double[] { double.Parse(tab[0]), double.Parse(tab[1]) };
}
set
{
this.InternalData = string.Format("{0},{1}", value[0], value[1]);
}
}
[EditorBrowsable(EditorBrowsableState.Never)]
public string InternalData { get; set; }
Thank you all for your inputs, due to your help I was able to track down the best way to solve this. Which is:
public string InternalData { get; set; }
public double[] Data
{
get
{
return Array.ConvertAll(InternalData.Split(';'), Double.Parse);
}
set
{
_data = value;
InternalData = String.Join(";", _data.Select(p => p.ToString()).ToArray());
}
}
Thanks to these stackoverflow posts:
String to Doubles array and
Array of Doubles to a String
I know it is a bit expensive, but you could do this
class Primitive
{
public int PrimitiveId { get; set; }
public double Data { get; set; }
[Required]
public Reference ReferenceClass { get; set; }
}
// This is the class that requires an array of doubles
class Reference
{
// Other EF stuff
// EF-acceptable reference to an 'array' of doubles
public virtual List<Primitive> Data { get; set; }
}
This will now map a single entity (here 'Reference') to a 'list' of your Primitive class. This is basically to allow the SQL database to be happy, and allow you to use your list of data appropriately.
This may not suit your needs, but will be a way to make EF happy.
It would be far easier if you use List<double> rather then double[]. You already have a table that stores your Data values. You probably have foreign key from some table to the table where your double values are stored. Create another model that reflects the table where doubles are stored and add foreign key mappings in the mappings class. That way you will not need to add some complex background logic which retrieves or stores values in a class property.
In my opinion almost all other answers work on the opposite of how it should be.
Entity EF should manage the string and the array must be generated from it. So the array must be whole read and written only when the string is accessed by EF.
A solution involving logic on Data[] is wrong because, as I wrote in a comment, you would run into paradoxical conditions. In all other conditions the variable must remain a pure array.
By putting the "get" and "set" logic in Data[], as I've seen so far, this happens:
1 - Every time an index access is made to the array, the array is automatically recreated from the string. This is a useless work, think of an iteration in a loop...
2 - when you go to set a single element it is not stored because it passes through "get" and not "set".
If you try to declare Data=new []{0,0,0} then set Data[1]=2 , going to re-read Data[1] the result is 0.
My solution is to completely turn the logic around.
public string Data_string
{
get => string.Join(';', Data??Array.Empty());
set => Data= value == null ? Array.Empty<double>() : Array.ConvertAll(value.Split(';',StringSplitOptions.RemoveEmptyEntries), double.Parse);
}
[NotMapped]
public double[] Data {get;set;}
Obviously this only applies to storing and retrieving data on databases, access to Data_string is exclusive to EF.
Once the string is read from the DB it is associated to Data_string which, through set, creates the Data array.
At this point you can work on Data without affecting the string in any way, like a normal array.
When you will ask EF to save in the DB, through the get in the Data_string property, the string will be completely reconstructed based on the Data elements and then stored as a string.
Practically the string is modified only twice, at the moment of reading from the DB and at the moment of saving.
In my opinion this solution is much more efficient than operating continuously on the string.
Nathan White has the best answer (got my vote).
Here is a small improvement over Joffrey Kern's answer to allow lists of any length (untested):
[NotMapped]
public IEnumerable<double> Data
{
get
{
var tab = InternalData.Split(',');
return tab.Select(double.Parse).AsEnumerable();
}
set { InternalData = string.Join(",", value); }
}
[EditorBrowsable(EditorBrowsableState.Never)]
public string InternalData { get; set; }
Don't use double[] use List insted.
Like this.
public class MyModel{
...
public List<MyClass> Data { get; set; }
...
}
public class MyClass{
public int Id { get; set; }
public double Value { get; set; }
}
All that solution that I see there are bad, because:
If you create table, you don't want to store data like this: "99.5,89.65,78.5,15.5" that's not valid! Firstly its a string that means if you can type letter into it and at the moment when your ASP.NET server call double.Parse it will result in FormatException and that you really don't want!
It's slower, because your server must parse the string. Why parse the string instead getting almost ready data from SQL Server to use?
i know this post is Ancient, but in case someone still needs to do something like this, PLEASE DO NOT USE THE ABOVE SOLUTIONS,
as the above solutions are EXTREMELY inefficient (Performance and Disk Space wise).., the best way is to store the array as a Byte array
public byte[] ArrayData;
[NotMapped]
public double[] Array {
get {
var OutputArray = new double[ArrayData.Length / 8];
for (int i = 0;i < ArrayData.Length / 8;i++)
OutputArray[i] = BitConverter.ToDouble(ArrayData, i * 8);
return OutputArray;
}
set {
var OutputData = new byte[value.Length * 8];
for (int i = 0;i < value.Length;i++) {
var BinaryValue = BitConverter.GetBytes(value[i]);
OutputData[(i*8)] = BinaryValue[0];
OutputData[(i*8)+1] = BinaryValue[1];
OutputData[(i*8)+2] = BinaryValue[2];
OutputData[(i*8)+3] = BinaryValue[3];
OutputData[(i*8)+4] = BinaryValue[4];
OutputData[(i*8)+5] = BinaryValue[5];
OutputData[(i*8)+6] = BinaryValue[6];
OutputData[(i*8)+7] = BinaryValue[7];
}
ArrayData = OutputData;
}
}
`
And if you need more performance, you can go for Unsafe code and use pointers .. instead of BitConverter ..
This is way better than saving double values (that can get huge) as string, then spliting the string array !! and then parsing the strings to double !!!
These getter/setters work on the whole array, but if you need to get just one item from the array, you can make a function that gets a single item from the array with a complexity of O(1) :
for Get :
public double Array_GetValue(int Index) {
return BitConverter.ToDouble(ArrayData, Index * 8);
}
for Set :
public void Array_SetValue(int Index, double Value) {
var BinaryValue = BitConverter.GetBytes(Value);
ArrayData[(Index*8)] = BinaryValue[0];
ArrayData[(Index*8)+1] = BinaryValue[1];
ArrayData[(Index*8)+2] = BinaryValue[2];
ArrayData[(Index*8)+3] = BinaryValue[3];
ArrayData[(Index*8)+4] = BinaryValue[4];
ArrayData[(Index*8)+5] = BinaryValue[5];
ArrayData[(Index*8)+6] = BinaryValue[6];
ArrayData[(Index*8)+7] = BinaryValue[7];
}
If your collection can be null or empty, and you want this to be preserved, do this:
[NotMapped]
public double[] Data
{
get => InternalData != null ? Array.ConvertAll(Data.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries), double.Parse) : null;
set => InternalData = value != null ? string.Join(";", value) : null;
}
Also, specify [Column(TypeName = "varchar")] on the string property for a more efficient storage data type.
A perfect enhancement to #Jonas's answer will be to add the necessary annotations. So, a cleaner version would be
[EditorBrowsable(EditorBrowsableState.Never)]
[JsonIgnore]
public string InternalData { get; set; }
[NotMapped]
public double[] Data
{
get => Array.ConvertAll(InternalData.Split(';'), double.Parse);
set
{
InternalData = string.Join(";", value.Select(p => p.ToString(CultureInfo.InvariantCulture)).ToArray());
}
}
The [JsonIgnore] Annotation will ignore the InternalData field from JSON serialization and Swagger UI.
[EditorBrowsable(EditorBrowsableState.Never)] will hide the public method from the IDE IntelliSense
So i am trying to retrieve an instance of the class "Sugar" for a specific date using this method in my UserDatabse.cs class:
public List<Sugar> GetSugarDate(DateTime dt)
{
var bld = database.Table<Sugar>().Where(mi => mi.Time.Date == dt.Date).ToList();
return bld;
}
*Keep in mind that the app doesn't have any instance of Sugar at the moment so the Date comparison is between a null and an actual date. I think that is causing the error, any solution would be appreciated.
The call to this method is made like this in another class:
DateTime Time = DateTime.Now;
ObservableCollection<Image> Sugar_Count = new ObservableCollection<Image>();
Image s = new Image();
s.Source = "drawable/soda.png";
var xa = App.Database.GetSugarDate(Time);
The class Sugar.cs is defined as follows:
public class Sugar
{
[PrimaryKey, AutoIncrement]
public int Id { get; set; }
public DateTime Time { get; set; }
public int DrinkCount { get; set; }
public Sugar()
{
Time = DateTime.Now;
DrinkCount = 0;
}
}
Now the error is get is as follows:
System.NotSupportedException: Member access failed to compile expression at SQLite.TableQuery'1[T].CompileExpr(System.Linq.Expressions.Expression expr, System.Collections.Generic.List'1[T]queryArgs)[0x006cc]in <9b4aaa861238418bec74a2ddde70f09>:0 at SQLite.TableQuery'1[T].CompileExpr(System.Linq.Expressions.Expression expr, System.Collections.Generic.List'1[T]queryArgs)[0x0009d]in <9b4aaa861238418bec74a2ddde70f09>:0 at SQLite.TableQuery'1[T].CompileExpr(System.Linq.Expressions.Expression expr, System.Collections.Generic.List'1[T]queryArgs)[0x0005f]in <9b4aaa861238418bec74a2ddde70f09>:0 at SQLite.TableQuery'1[T].CompileExpr(System.Linq.Expressions.Expression expr, System.Collections.Generic.List'1[T]queryArgs)[0x00008]in <9b4aaa861238418bec74a2ddde70f09>:0 at
System.Collections.Generic.List'1[T]..ctor(System.Collections.Generic.IEnumerable'1[T]collection)[0x00062] in /Users/builder/jenkins/workspace/xamarin-android/external/mono/mcs/class/referencesource/generic/list.cs:98 .....
The error occurs at this specific line:
var bld = database.Table<Sugar>().Where(mi => mi.Time.Date == dt.Date).ToList();
Where am i going wrong?
This part of the expression can not be translated to SQL.
mi => mi.Time.Date
You can try using:
var bld = database.Table<Sugar>().ToList().Where(mi => mi.Time.Date == dt.Date).ToList();
Accessing to the Date part of a DateTime column (mi.Time.Date) can not be translated to SQL using Linq, for this reason, your statement failed initially. So, using ToList fetches all records in memory allowing us to query with Linq to Object method not Linq to SQLite.
Its a little janky, but I have got this to work:
public List<Sugar> GetSugarDate(DateTime dt)
{
var dayStart = dt.Date.AddDays(-1);
var dayEnd = dt.Date.AddDays(1);
var bld = database.Table<Sugar>().Where(mi => mi.Time > dayStart && mi.Time < dayEnd).ToList();
return bld;
}
Also make sure you initialize your database connection with:
SQLiteConnection database = new SQLiteConnection(_path,false);
If you are querying a nullable DateTime
The little janky code worked for me
var dayStart = stockDate.Date.AddDays(-1);
var dayEnd = stockDate.Date.AddDays(1);
return db.Table<ProductStock>().Where(x => x.StockDate > dayStart && x.StockDate < dayEnd).ToListAsync();
I am trying to setup a product key system in my application, but I want to ensure the attribute has the right size (16 characters).
I tried the following
public class ProductKey
{
public const int ProductKeyLength = 16;
[StringLength(ProductKeyLength, MinimumLength = ProductKeyLength)]
private string _value;
[Required]
[Index(IsUnique = true)]
public string Value {
get
{
var temp = Regex.Replace(this._value, ".{4}", "$0-");
return temp.Trim('-');
}
set { this._value = value.Replace("-", "");}
}
}
I want to enable the user to insert the key with our without hyphen. I get the following error with above code:
Column 'Value' in table 'dbo.ProductKeys' is of a type that is invalid for use as a key column in an index.
As I understood, I need to set a limit to Value so it can be used as a unique key. But, _value has a limit and _value is the actual representation of Value in the database.
Is there a way to set the limit correctly in this case?
Thanks in advance.
You are getting the error because without a StringLength attribute on the Value field, the database column gets created as VARCHAR(MAX) which cannot be used as a key. You need a [StringLength] on the field being used as a key. However, as your getter is returning the key formatted with dashes, you need the key length to be 19:
public class ProductKey
{
public const int ProductKeyLength = 19;
private string _value { get; set; }
[Key]
[Required]
[StringLength(ProductKeyLength, MinimumLength = ProductKeyLength)]
[Index(IsUnique = true)]
public string Value
{
get
{
var temp = Regex.Replace(this._value, ".{4}", "$0-");
return temp.Trim('-');
}
set { this._value = value.Replace("-", ""); }
}
}
You might be better off doing your format conversion in ViewModels and client-side code, as one problem you'll have here is searching - for example...
db.Keys.Add(new ProductKey { Value = "1234-5678-9012-3456" });
db.Keys.Add(new ProductKey { Value = "1234567890123455" });
db.SaveChanges();
Console.WriteLine(db.Keys.Count(k => k.Value.Contains("89"))); // 0
Console.WriteLine(db.Keys.Count(k => k.Value.Contains("8-9"))); // 2
here is the repository:
#Query(value = "select u.balance from User u where u.name=:name")
float toGetBalance(#Param("name") String name);
and here is the DAO interface:
boolean checkBalance(String userName, float totalPrice);
and here is the service
#Transactional(readOnly = true)
#Override
public boolean checkBalance(String userName, float totalPrice) {
if (userRepository.toGetBalance(userName) < totalPrice) {
return false;
} else {
return true;
}
}
and here is the error info:
org.springframework.aop.AopInvocationException: Null return value from advice does not match primitive return type for: public abstract float com.repository.UserRepository.toGetBalance(java.lang.String)
and the type of balance is float!
what's wrong?
Change the signature of your repository to
#Query(value = "select u.balance from User u where u.name=:name")
Float toGetBalance(#Param("name") String name);
And it will simply return null if there is no such user in database with given name
#Query(value = "select u.balance from User u where u.name=:name")'
'Float toGetBalance(#Param("name") String name);
This exception arise because name not exist OR balance = NULL fpr the selected record in the table
So the query results no output. Spring JPA not able to bind the result with Return type Float.
Null return value from advice does not match primitive return type for: public abstract float com.repository.UserRepository.toGetBalance(java.lang.String)
I am using JSON.Net to serialize my objects. For eg, if this is my object
Class MainData
{
[JsonProperty("keyValues")]
string val;
}
the data for 'val' is a key value pair string like this key1:value1.
I have a scenario where I should not get the above 'keyValues' name in my final serialized string and instead get a serialized string which looks like this
{
"key1":"value1"
}
Currently with my serializer I am getting this, which is not what I need
{
"keyValues":"key:value1"
}
Can somebody guide me to any documentation/solution to dynamically assign the name of the field instead of using the default variable name/JSONProperty Name defined inside the object?
Thanks a lot in advance.
I've been struggling with this all day, what I've done is used a dictionary object and serialised this
however I had an error message that was "cannot serialise dictionary", should have read the whole message, "cannot serialise dictionary when the key is not a string or object"
this now works for me and gives me a key/value pair
i have the following objects
public class Meal {
public int mealId;
public int value;
public Meal(int MealId, int Value) {
mealId = MealId;
value = Value;
} }
public class Crew
{
public Meal[] AllocatedMeals {
get {
return new Meal[]{
new Meal(1085, 2),
new Meal(1086, 1) }; } }
public int AllocatedMealTotal {
get {
return this.AllocatedMeals.Sum(x => x.value); } }
}
then the following code
Dictionary<string,string> MealsAllocated = crew.AllocatedMeals.ToDictionary(x => x.mealId.ToString(), x => x.value.ToString());
return new JavaScriptSerializer().Serialize(
new {
Allocated = new {
Total = crew.AllocatedMealTotal,
Values = MealsAllocated } )
to get
"Allocated":{"Total":3,"Values":{"1085":"2","1086":"1"}}