fix concurrency issue when adding a new step to the same tactic

DbServices/DbTacticService.cs

@@ -9,6 +9,7 @@ namespace DbServices;
 
 public class DbTacticService(AppContext.AppContext context) : ITacticService
 {
+
     public Task<IEnumerable<Tactic>> ListTacticsOf(int userId)
     {
         return Task.FromResult(
@@ -111,25 +112,33 @@ public class DbTacticService(AppContext.AppContext context) : ITacticService
 
     public async Task<int?> AddTacticStep(int tacticId, int parentStepId, string initialJson)
     {
-        if (!context.Tactics.Any(t => t.Id == tacticId))
+
+        var tactic = await context.Tactics.FirstOrDefaultAsync(t => t.Id == tacticId);
+        if (tactic == null)
         {
             return null;
         }
 
-        var nextStepId = context.TacticSteps
+        TacticStepEntity entity;
-            .Where(s => s.TacticId == tacticId)
+        int nextStepId;
-            .Max(s => s.StepId) + 1;
+        lock (tactic)
-
-        var entity = new TacticStepEntity
         {
-            JsonContent = initialJson,
+            nextStepId = context.TacticSteps
-            ParentId = parentStepId,
+                .Where(s => s.TacticId == tacticId)
-            TacticId = tacticId,
+                .Max(s => s.StepId) + 1;
-            StepId = nextStepId
+
-        };
+            entity = new TacticStepEntity
+            {
+                JsonContent = initialJson,
+                ParentId = parentStepId,
+                TacticId = tacticId,
+                StepId = nextStepId
+            };
+
+            context.Add(entity);
+            context.SaveChanges();
+        }
 
-        await context.AddAsync(entity);
-        await context.SaveChangesAsync();
 
         return entity.StepId;
     }

WebAPI.sln

@@ -54,5 +54,9 @@ Global
 		{465819A9-7158-4612-AC57-ED2C7A0F243E}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{465819A9-7158-4612-AC57-ED2C7A0F243E}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{465819A9-7158-4612-AC57-ED2C7A0F243E}.Release|Any CPU.Build.0 = Release|Any CPU
+		{9C5EAD2F-FA50-43C2-BB86-1065ED661C52}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{9C5EAD2F-FA50-43C2-BB86-1065ED661C52}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{9C5EAD2F-FA50-43C2-BB86-1065ED661C52}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{9C5EAD2F-FA50-43C2-BB86-1065ED661C52}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 EndGlobal