Handle unique constraint violation on ProductCompanyTableCouple create

DrinkRateAPI/Services/ProductCompanyTableCoupleService.cs

@@ -4,6 +4,7 @@ using DrinkRateAPI.Contexts;
 using DrinkRateAPI.DbEntities;
 using DrinkRateAPI.Exceptions;
 using Microsoft.EntityFrameworkCore;
+using Npgsql;
 
 namespace DrinkRateAPI.Services;
 
@@ -24,7 +25,20 @@ public class ProductCompanyTableCoupleService(ApplicationDbContext context)
         };
 
         _context.CompanyTable.Add(companyTable);
-        await _context.SaveChangesAsync();
+
+        try
+        {
+            await _context.SaveChangesAsync();
+        }
+        catch (DbUpdateException ex) when
+            (ex.InnerException is PostgresException
+                {
+                    SqlState: PostgresErrorCodes.UniqueViolation
+                }
+            )
+        {
+            throw new BadRequestException("Product table or company table with the same name already exists.");
+        }
 
         return await GetProductCompanyTableCouplePostResponse(
             productCompanyTableCouplePost.ProductTableName,