c# - Entity Framework Many-to-Many update without creating duplicates? -

i using entity framework (code-first) create database, part of contains 2 entities many-to-many relationship. here code:

public class product {     [key]     public int productid { get; set; }      [maxlength(50)]     public string cusip { get; set; }      [maxlength(50)]     public string sedol { get; set; }      [maxlength(50)]     public string buid { get; set; }      [maxlength(50)]     public string key { get; set; }      [required]     public bool track { get; set; }      [inverseproperty("products")]     [foreignkey("productlistid")]     public virtual list<productlist> productlists { get; set; }      public override string tostring()     {         return string.format("product[ productid: {0}, cusip: {1}, sedol: {2}, buid: {3}, key: {4}, track: {5}, productlists: {6} ]",                             productid,                             cusip,                             sedol,                             buid,                             key,                             track,                             (productlists != null ? ""+productlists.count : "null"));     } }  public class productlist {     [key]     public int productlistid { get; set; }      [required]     [maxlength(50)]     public string name { get; set; }      [inverseproperty("productlists")]     [foreignkey("productid")]     public virtual list<product> products { get; set; }      public override string tostring()     {         return string.format("product-list[ productlistid: {0}, name: {1}, products: {2} ]",                             productlistid,                              name,                             (products != null ? "" + products.count : "null"));     } } 

in repository, attempting write update method product, such changing tracking boolean or adding/removing productlist save database. using angularjs , asp.net-mvc rest of project, here update method in productscontroller class:

    public void put(int id, [frombody] product product)     {         _repo.updateproduct(id, product);         _repo.save();     } 

because called angularjs, product object initialized js object.

and finally, here's updateproduct method in repository:

    public bool updateproduct(int id, models.product product)     {         if (product != null) system.diagnostics.debug.writeline("updateproduct() [" + id + "]\n" + product.tostring());          if (id == 0) return addproduct(product);          try         {             product ctxproduct = getproduct(id);             if (ctxproduct != null && product != null)             {                 ctxproduct.cusip = product.cusip;                 ctxproduct.sedol = product.sedol;                 ctxproduct.buid = product.buid;                 ctxproduct.key = product.key;                 ctxproduct.track = product.track;                  /*ctxproduct.productlists = new list<productlist>();                 (int = 0; < product.productlists.count; i++)                 {                     ctxproduct.productlists.add((product.productlists[i].productlistid == 0)                                                 ? product.productlists[i]                                                 : getproductlistincludingproducts(product.productlists[i].productlistid));                  }*/                 return true;             }             return false;         }         catch (exception e)         {             system.diagnostics.debug.writeline(e.message + "\n ----- " + e.innerexception);             return false;         }     } 

right now, section should update productlist relations commented out. while it's this, can update other field in product , work expected.

if uncomment section, code create duplicate productlists in database, duplicates of products contained in lists.

lastly, if replace getproductlistincludingproducts(product.productlists[i].productlistid) getproductlist(product.productlists[i].productlistid), following error _repo.save():

system.data.sqlclient.sqlexception: violation of primary key constraint 'pk_dbo.productlistproducts'. cannot insert duplicate key in object 'dbo.productlistproducts' 

getproductlistincludingproducts() adds .include("products") in call context.

i update method readjust many many relationship without crashing or creating lot of duplicate data.

it took awhile figured out. turns out problem webapi formatter. code defaulting xmlmediaformatter - when expecting using jsonmediaformatter set handle reference tracking. in case helps anybody, here final updateproduct method works jsonmediaformatter:

    public bool updateproduct(int id, product product)     {         if (product != null) system.diagnostics.debug.writeline("updateproduct() [" + id + "] " + product.tostring());          if (id == 0) return addproduct(product);          try         {             product ctxproduct = getproductincludingproductlists(id);              if (ctxproduct != null && product != null)             {                 ctxproduct.cusip = product.cusip;                 ctxproduct.sedol = product.sedol;                 ctxproduct.buid = product.buid;                 ctxproduct.key = product.key;                 ctxproduct.track = product.track;                  ctxproduct.productlists = new list<productlist>();                 foreach (productlist pl in product.productlists)                     ctxproduct.productlists.add(pl.productlistid == 0                                                  ? pl                                                  : getproductlist(pl.productlistid));                 return true;             }             return false;         }         catch (exception e)         {             system.diagnostics.debug.writeline("update product error: " + e.message + "\ninner: " + e.innerexception);             return false;         }     }