Entity Framework - Code First - Can t Store List String

Question

I wrote such class   class Test        Key       DatabaseGeneratedAttribute DatabaseGeneratedOption Identity       public int Id   get  set         Required      public List lt String gt  Strings   get  set         public Test                 Strings   new List lt string gt                         test                test2                test3                test4                       and  internal class DataContext   DbContext       public DbSet lt Test gt  Tests   get  set        After run code   var db   new DataContext    db Tests Add new Test     db SaveChanges      my data is getting saved but just the Id  I don t have any tables nor relationships applying to Strings list    What am I doing wrong  I tried also to make Strings virtual but it didn t change anything   Thank you for your help

User · Answer

JSON NET to the rescue   You serialize it to JSON to persist in the Database and Deserialize it to reconstitute the  NET collection  This seems to perform better than I expected it to with Entity Framework 6  amp  SQLite  I know you asked for List lt string gt  but here s an example of an even more complex collection that works just fine   I tagged the persisted property with  Obsolete  so it would be very obvious to me that  this is not the property you are looking for  in the normal course of coding  The  real  property is tagged with  NotMapped  so Entity framework ignores it    unrelated tangent   You could do the same with more complex types but you need to ask yourself did you just make querying that object s properties too hard for yourself   yes  in my case    using Newtonsoft Json        NotMapped  public Dictionary lt string  string gt  MetaData   get  set      new Dictionary lt string  string gt           lt summary gt   lt see cref  MetaData   gt  for database persistence   lt  summary gt   Obsolete  Only for Persistence by EntityFramework    public string MetaDataJsonForDb       get               return MetaData    null     MetaData Any                        null                      JsonConvert SerializeObject MetaData              set               if  string IsNullOrWhiteSpace value              MetaData Clear            else            MetaData   JsonConvert DeserializeObject lt Dictionary lt string  string gt  gt  value

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Slightly tweaking  Mathieu Viales s answer  here s a  NET Standard compatible snippet using the new System Text Json serializer thus eliminating the dependency on Newtonsoft Json   using System Text Json   builder Entity lt YourEntity gt    Property p   gt  p Strings       HasConversion          v   gt  JsonSerializer Serialize v  default           v   gt  JsonSerializer Deserialize lt List lt string gt  gt  v  default      Note that while the second argument in both Serialize   and Deserialize   is typically optional  you ll get an error      An expression tree may not contain a call or invocation that uses   optional arguments   Explicitly setting that to the default  null  for each clears that up

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You can use this ScalarCollection container that confines an array and provides some manipulation options  Gist    Usage   public class Person       public int Id   get  set          will be stored in database as single string      public SaclarStringCollection Phones   get  set      new ScalarStringCollection        Code   using System Collections ObjectModel  using System ComponentModel  using System Linq   namespace System Collections Specialized    if NET462    ComplexType   endif   public abstract class ScalarCollectionBase lt T gt     if NET462     Collection lt T gt    else     ObservableCollection lt T gt   endif         public virtual string Separator   get        n       public virtual string ReplacementChar   get               public ScalarCollectionBase params T   values              if  values    null          foreach  var item in Items            Items Add item           if NET462      Browsable false    endif      EditorBrowsable EditorBrowsableState Never        Obsolete  Not to be used directly by user  use Items property instead         public string Data             get                 var data   Items Select item   gt  Serialize item             Replace Separator  ReplacementChar ToString              return string Join Separator  data Where s   gt  s  Length  gt  0                  set                 Items Clear            if  string IsNullOrWhiteSpace value             return           foreach  var item in value              Split new     Separator                   StringSplitOptions RemoveEmptyEntries  Select item   gt  Deserialize item              Items Add item                      public void AddRange params T   items              if  items    null          foreach  var item in items            Add item              protected abstract string Serialize T item       protected abstract T Deserialize string item          public class ScalarStringCollection   ScalarCollectionBase lt string gt          protected override string Deserialize string item    gt  item      protected override string Serialize string item    gt  item         public class ScalarCollection lt T gt    ScalarCollectionBase lt T gt      where T   IConvertible         protected override T Deserialize string item    gt         T Convert ChangeType item  typeof T        protected override string Serialize T item    gt  Convert ToString item

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I want to add that when using Npgsql  data provider for PostgreSQL   arrays and lists of primitive types are actually supported  https   www npgsql org efcore mapping array html

User · Answer

Entity Framework does not support collections of primitive types  You can either create an entity  which will be saved to a different table  or do some string processing to save your list as a string and populate the list after the entity is materialized

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I Know this is a old question  and Pawel has given the correct answer  I just wanted to show a code example of how to do some string processing  and avoid an extra class for the list of a primitive type   public class Test       public Test                  strings   new List lt string gt                         test                test2                test3                test4                         Key       DatabaseGenerated DatabaseGeneratedOption Identity       public int Id   get  set         private List lt String gt   strings   get  set         public List lt string gt  Strings               get   return  strings            set    strings   value                Required      public string StringsAsString               get   return String Join       strings             set    strings   value Split      ToList

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Of course Pawel has given the right answer  But I found in this post that since EF 6  it is possible to save private properties  So I would prefer this code  because you are not able to save the Strings in a wrong way   public class Test        Key       DatabaseGenerated DatabaseGeneratedOption Identity       public int Id   get  set          Column       Required      private String StringsAsStrings   get  set         public List lt String gt  Strings               get   return StringsAsStrings Split      ToList              set                       StringsAsStrings   String Join      value                       public Test                 Strings   new List lt string gt                         test                test2                test3                test4

User · Answer

Just to simplify -  Entity framework doesn t support primitives  You either create a class to wrap it or add another property to format the list as a string   public ICollection lt string gt  List   get  set    public string ListString       get   return string Join      List         set   List   value Split      ToList

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This answer is based on the ones provided by  Sasan and  CAD bloke  If you wish to use this in  NET Standard 2 or don t want Newtonsoft  see Xaniff s answer below Works only with EF Core 2 1   not  NET Standard compatible  Newtonsoft JsonConvert  builder Entity lt YourEntity gt    Property p   gt  p Strings       HasConversion          v   gt  JsonConvert SerializeObject v           v   gt  JsonConvert DeserializeObject lt List lt string gt  gt  v     Using the EF Core fluent configuration we serialize deserialize the List to from JSON  Why this code is the perfect mix of everything you could strive for   The problem with Sasn s original answer is that it will turn into a big mess if the strings in the list contains commas  or any character chosen as the delimiter  because it will turn a single entry into multiple entries but it is the easiest to read and most concise  The problem with CAD bloke s answer is that it is ugly and requires the model to be altered which is a bad design practice  see  Marcell Toth s comment on Sasan s answer   But it is the only answer that is data-safe

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EF Core 2 1    Property  public string   Strings   get  set     OnModelCreating  modelBuilder Entity lt YourEntity gt                 Property e   gt  e Strings               HasConversion                  v   gt  string Join      v                   v   gt  v Split      StringSplitOptions RemoveEmptyEntries     Update  2021-02-14  The PostgreSQL has an array data type and the Npgsql EF Core provider does support that  So it will map your C  arrays and lists to the PostgreSQL array data type automatically and no extra config is required  Also you can operate on the array and the operation will be translated to SQL  More information on this page

[c#] Entity Framework - Code First - Can't Store List<String>

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