ef-core-3.1

问题 Is there any way to query with EFCore 3.1 by joining multiple fields together with String.Format, or $"{}" or just the traditional "" + "" + ""? I have this code: await this.Db.ACoolDbSet.Where(y => y.Plums + " " + y.Pears == "LOL").ToListAsync(); Plums and Pears are integers. It results in this error: System.InvalidOperationException: 'Null TypeMapping in Sql Tree' Is this expected? This exception was originally thrown at this call stack: Microsoft.EntityFrameworkCore.Query

问题 Is there any way to query with EFCore 3.1 by joining multiple fields together with String.Format, or $"{}" or just the traditional "" + "" + ""? I have this code: await this.Db.ACoolDbSet.Where(y => y.Plums + " " + y.Pears == "LOL").ToListAsync(); Plums and Pears are integers. It results in this error: System.InvalidOperationException: 'Null TypeMapping in Sql Tree' Is this expected? This exception was originally thrown at this call stack: Microsoft.EntityFrameworkCore.Query

问题 I need to get top 10 rows for each group in a table with entity framework. Based on other solution on SO, I tried 2 things: var sendDocuments = await context.Set<DbDocument> .Where(t => partnerIds.Contains(t.SenderId)) .GroupBy(t => t.SenderId) .Select(t => new { t.Key, Documents = t.OrderByDescending(t2 => t2.InsertedDateTime).Take(10) }) .ToArrayAsync(); error: System.InvalidOperationException: 'The LINQ expression '(GroupByShaperExpression: KeySelector: (d.SenderId), ElementSelector:

问题 I need to execute a complex sql query in entity framework core 3.1.1, on researching i found out that keyless entity types is the way to go in code first approach. I see lot of documents for dbquery but this is marked as obsolete in .net core 3.x keyless entity types As per Microsoft documentation it says dbquery is obsolete so use dbset approach instead, but with dbset it is trying to create a new table in database. how to disable table generation in keyless entity types while applying

问题 Consider the following class. It tries to protect the access to the _assignedTrays . Actually, it works perfectly, since EF automatically links the backing field _assignedTrays to the property AssignedTrays - by convention (msdn) public class Rack { private List<Tray> _assignedTrays = new List<Tray>(); private Rack() { } public Rack(string rackId) { this.Id = rackId; } public string Id { get; private set; } public IReadOnlyList<Tray> AssignedTrays => this._assignedTrays.AsReadOnly(); public

问题 Consider the following class. It tries to protect the access to the _assignedTrays . Actually, it works perfectly, since EF automatically links the backing field _assignedTrays to the property AssignedTrays - by convention (msdn) public class Rack { private List<Tray> _assignedTrays = new List<Tray>(); private Rack() { } public Rack(string rackId) { this.Id = rackId; } public string Id { get; private set; } public IReadOnlyList<Tray> AssignedTrays => this._assignedTrays.AsReadOnly(); public

问题 This question already has an answer here : Problem with EF OrderBy after migration to .net core 3.1 (1 answer) Closed 27 days ago . In MS SQL Server I have a table that contains a history of calls to contacts (that is another table). Accessed by EF, The Entities are the following: public partial class CallbackHistory { public int HistoryId { get; set; } public int CompanyId { get; set; } public int CallerId { get; set; } public DateTime LastCallTimeStamp { get; set; } public virtual

问题 Consider this code: _dbContext.Messages .GroupBy(m => new { MinId = m.SenderId <= m.RecipientId ? m.SenderId : m.RecipientId, MaxId = m.SenderId > m.RecipientId ? m.SenderId : m.RecipientId }) .Select(gm => gm.OrderByDescending(m => m.SentAt).FirstOrDefault()); By this I group all dialogues of users by their Id's no matter who sent the message. Then I order messages by SentAt date inside the groups and select one last message out of each dialogue. The thing is that this code worked and more

问题 Consider this code: _dbContext.Messages .GroupBy(m => new { MinId = m.SenderId <= m.RecipientId ? m.SenderId : m.RecipientId, MaxId = m.SenderId > m.RecipientId ? m.SenderId : m.RecipientId }) .Select(gm => gm.OrderByDescending(m => m.SentAt).FirstOrDefault()); By this I group all dialogues of users by their Id's no matter who sent the message. Then I order messages by SentAt date inside the groups and select one last message out of each dialogue. The thing is that this code worked and more