EF核心无法创建表，sql语法错误

Question

我是 Entity 框架的新手，我不明白为什么它会给我一个 sql 语法错误，我认为使用 EFCore 的全部目的是处理 sql 语法并将所有 sql 查询抽象出来

这是我的模型：

  class Block 
    {
        public BlockHeader Header {get ;}
        public List<Transaction> Transactions {get;}

        public Block(List<Transaction> transactions, BlockHeader header)
        {
            Transactions= transactions;
            Header=header;           
        }    
        public Block(){
            
        }
    }
    public class BlockHeader
    {
        public byte[] Hash {get ;} 
        public byte[]  PreviousHash { get; }
        public DateTime timestamp { get; }
        public int version{ get; } 
        public byte[] MerkleRoot{ get; }
        public int SequenceNumber {get ; private set;}

        public BlockHeader (byte[] previoushash,int sequencenumber,List<Transaction> transactions)
        {
            timestamp = DateTime.Now;
            PreviousHash =  previoushash;
            version = 1;
            SequenceNumber = sequencenumber;
            MerkleRoot = ComputeMerkleRoot(transactions);
            Hash = ComputeBlockHash();

        }

这是我的数据库上下文类

        class BlockchainDB : DbContext
        {
            public BlockchainDB()
            {
                
            }

            protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            {
                optionsBuilder.UseMySQL("server=localhost;database = Blockchain ;user = root ; password = password");
            }
            protected override void OnModelCreating(ModelBuilder builder){
                builder.Entity<Block>(e => e.HasNoKey());
            }   
        }

当我添加迁移时，它会成功添加，但是当我使用此命令更新数据库时

dotnet ef database update

它输出这个错误：

Failed executing DbCommand (2ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
CREATE TABLE `Block` (

);
MySql.Data.MySqlClient.MySqlException (0x80004005): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 3

Answer 1

EFCore 实体需要设置器，否则不会设置引用。

我建议你写这样的东西来确保封装

public class Block 
{
  protected Block()
  {
    // empty constructor needed for EF Core
  }

  // Navigation properties 
  public virtual BlockHeader BlockHeader {get; private set;}

  // For collections 
  private readonly List<ChildEntity> _children = new List<ChildEntity>();
  public virtual IReadOnlyList<ChildEntity> Children => _children.ToList();

  // Encapsulated Business logic constructor 
  public Block(BlockHeader header, List<ChildEntity> children)
  {
    _children = children;
    BlockHeader = header;
  }
}

您也可以通过实体核心框架使用fluent api modelbuilder配置并显式映射关系。