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
I've declared an API call in an interface and was wondering if it is possible to put constraints on some of the parameters. The API I'm accessing has these constraints as well and would like to enforce them in my program.
#GET("/recipes/search")
Call<RecipeResponse> getRecipes(
#Query("cuisine") String cuisine,
#Query("diet") String diet,
#Query("excludeIngredients") String excludeIngredients,
#Query("intolerances") String intolerances,
#Query("number") Integer number,
#Query("offset") Integer offset,
#Query("query") String query,
#Query("type") String type
);
How can I do this?
I know that it is possible to do this with POST request, and passing along an object via the RequestBody through the #Body annotation. Can I do this with a GET request too, where information is passed via the query string?
Thanks!
I think I ended up finding a solution. I've made a class SearchRecipeRequest in which I declare all possible parameters as class variables. In the setters I do the data validation such as checking for null on parameters that are required, or min/max value constraints on integers as specified by the endpoint. I then made a SearchRecipeRequestBuilder class to build such an object like so to make it easier to deal with all those possible parameters:
public class SearchRecipeRequestBuilder {
private String _cuisine = null,
_diet = null,
_excludeIngredients = null,
_intolerances = null,
_query = null,
_type = null;
private Integer _number = null,
_offset = null;
public SearchRecipeRequestBuilder() {}
public SearchRecipeRequest buildRequest() {
return new SearchRecipeRequest(_cuisine, _diet, _excludeIngredients, _intolerances, _number, _offset, _query, _type);
}
public SearchRecipeRequestBuilder cuisine(String cuisine) {
_cuisine = cuisine;
return this;
}
public SearchRecipeRequestBuilder diet(String diet) {
_diet = diet;
return this;
}
public SearchRecipeRequestBuilder excludeIngredients(String excludeIngredients) {
_excludeIngredients = excludeIngredients;
return this;
}
public SearchRecipeRequestBuilder intolerances(String intolerances) {
_intolerances = intolerances;
return this;
}
public SearchRecipeRequestBuilder query(String query) {
_query = query;
return this;
}
public SearchRecipeRequestBuilder type(String type) {
_type = type;
return this;
}
public SearchRecipeRequestBuilder number(Integer number) {
_number = number;
return this;
}
public SearchRecipeRequestBuilder offset(Integer offset) {
_offset = offset;
return this;
}
}
Which allows me to build the request like so:
SearchRecipeRequest request = new SearchRecipeRequestBuilder()
.query("burger")
.buildRequest();
I then pass along that object to a different function that knows how to use the request object to pass it along to the API.
That's how I'm doing it right now, if someone has a better way I'd love to hear it. :)
I got the idea to use the Builder pattern from a different StackOverflow question: Managing constructors with many parameters in Java.
I Have a model like this
public partial class TableNames
{
public string Name { get; set; }
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.None)]
public int IntId { get; set; }
}
Then in a controller I'm Trying to get max IntIdfrom that model
var max = from c in db.TableNames
select c;
int? Max = max.AsQueryable().Max(x => x.IntId); //This isntruction throws an error
int IntId = ( Max == null ? 1 : Max + 1);
When the table has no records (it's empty) , the controller throws this error
The cast to value type 'Int32' failed because the materialized value is null.
Either the result type's generic parameter or the query must use a nullable type.
How can I do to fix it ?
Try this instead:
int? Max = max.AsQueryable().Max(x => (int?)x.IntId);
If you do not wish to deal with Nullable and want a default value (based upon Splendor's code), you may do something similar to the following:
int Max = max.AsQueryable().Max(x => (int?)x.IntId) ?? 1;
try:
max.Where(i => i.IntId.HasValue).Select(i => i.IntId.Value).Max()
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"}}
I have declared my c# application constant this way:
public class Constant
public struct profession
{
public const string STUDENT = "Student";
public const string WORKING_PROFESSIONAL = "Working Professional";
public const string OTHERS = "Others";
}
public struct gender
{
public const string MALE = "M";
public const string FEMALE = "F";
}
}
My validation function:
public static bool isWithinAllowedSelection(string strValueToCheck, object constantClass)
{
//convert object to struct
//loop thru all const in struct
//if strValueToCheck matches any of the value in struct, return true
//end of loop
//return false
}
During runtime, I will like pass in the user inputted value and the struct to check if the value exist in the struct. The struct can be profession and gender. How can I achieve it?
Example:
if(!isWithinAllowedSelection(strInput,Constant.profession)){
response.write("invalid profession");
}
if(!isWithinAllowedSelection(strInput,Constant.gender)){
response.write("invalid gender");
}
You probably want to use enums, not structs with constants.
Enums gives you a lot of possibilities, it is not so hard to use its string values to save it to the database etc.
public enum Profession
{
Student,
WorkingProfessional,
Others
}
And now:
To check existence of value in Profession by value's name:
var result = Enum.IsDefined(typeof(Profession), "Retired"));
// result == false
To get value of an enum as a string:
var result = Enum.GetName(typeof(Profession), Profession.Student));
// result == "Student"
If you really can't avoid using value names with whitespaces or other special characters, you can use DescriptionAttribute:
public enum Profession
{
Student,
[Description("Working Professional")] WorkingProfessional,
[Description("All others...")] Others
}
And now, to get description from Profession value you can use this code (implemented here as an extension method):
public static string Description(this Enum e)
{
var members = e.GetType().GetMember(e.ToString());
if (members != null && members.Length != 0)
{
var attrs = members.First()
.GetCustomAttributes(typeof(DescriptionAttribute), false);
if (attrs != null && attrs.Length != 0)
return ((DescriptionAttribute) attrs.First()).Description;
}
return e.ToString();
}
This method fetches description defined in attribute and if there's none, returns value name. Usage:
var e = Profession.WorkingProfessional;
var result = e.Description();
// result == "Working Professional";