扩展entity framework core实现默认字符串长度,decimal精度,entity自动注册和配置
文章以efcore 2.0.0-preview2.测试验证通过。其他版本不保证使用，但是思路不会差太远。源代码,报道越短，事情越严重！文章越短，内容越精悍！
目标：
1.实现entity的自动发现和mapper设置.
2.默认字符串长度，而不是nvarchar(max).
3.decimal设置精度
实现目标1：继承RelationalModelCustomizer，重写Customize方法。
当然，我们也可以重写dbcontext的OnModelCreating方法，but，我们怎么能这么low呢。必须要用点高级玩意是吧，当然这也是更底层的扩展方式。项目里面有多个dbcontext的话，在这里集中扩展管理比较方便。
在然后，这个RelationalModelCustomizer继承自ModelCustomizer。在联想到efcore未来的版本会支持redis，nosql什么的。到时候估计还回有一个osqlModelCustomizer之类的吧，期待中......
实现目标2、3：继承自CoreConventionSetBuilder类，重写CreateConventionSet方法。
重写CreateConventionSet方法，能拿到关键的ConventionSet对象。这个对象囊括了诸多的约定配置等等。比如maxlengthattribute属性标记，stringlength属性标记，timestamp属性标记，表id的自动发现规则等等等。。。
那，我们增加2个小小的约定：字符串默认长度（StringDefaultLengthConvention），和decimal精度设置attribute(DecimalPrecisionAttributeConvention)及fluntapi方式.
文章的最后附efcore 所有的可替换扩展service。
//servie,DI注入替换.services.AddSingleton();
services.AddSingleton();
//实现entity的自动发现和mapper设置
public class MyRelationalModelCustomizer : RelationalModelCustomizer{
public MyRelationalModelCustomizer(ModelCustomizerDependencies dependencies) : base(dependencies){}
public override void Customize(ModelBuilder modelBuilder, DbContext dbContext) {
base.Customize(modelBuilder, dbContext);
var sp = (IInfrastructure)dbContext;
var dbOptions = sp.Instance.GetServices(); foreach (var item in dbOptions)
{
if (item.ContextType == dbContext.GetType())
ConfigureDbContextEntityService.Configure(modelBuilder, item, dbContext);
}
}
}
public class MyCoreConventionSetBuilder : CoreConventionSetBuilder{
public MyCoreConventionSetBuilder(CoreConventionSetBuilderDependencies dependencies) : base(dependencies){}
public override ConventionSet CreateConventionSet() {
var conventionSet = base.CreateConventionSet();
//默认字符串长度，而不是nvarchar(max).
//为什么要insert(0,obj),则是因为这个默认规则要最优先处理，如果后续有规则的话就直接覆盖了。
//propertyBuilder.HasMaxLength(32, ConfigurationSource.Convention);
//理论上我指定了规则的级别为.Convention，应该和顺序就没有关系了。but，还没有完成测试，所以我也不知道
conventionSet.PropertyAddedConventions.Insert(0, new StringDefaultLengthConvention()); //decimal设置精度
conventionSet.PropertyAddedConventions.Add(new DecimalPrecisionAttributeConvention());
return conventionSet;
}
} 下面是StringDefaultLengthConvention和DecimalPrecisionAttributeConvention的实现代码
//字符串默认长度
public class StringDefaultLengthConvention : IPropertyAddedConvention
{
public InternalPropertyBuilder Apply(InternalPropertyBuilder propertyBuilder) {
if (propertyBuilder.Metadata.ClrType == typeof(string))
propertyBuilder.HasMaxLength(32, ConfigurationSource.Convention);
return propertyBuilder;
}
}
//attribute方式设置decimal精度
public class DecimalPrecisionAttributeConvention : PropertyAttributeConvention
{
public override InternalPropertyBuilder Apply(InternalPropertyBuilder propertyBuilder, DecimalPrecisionAttribute attribute, MemberInfo clrMember) {
if (propertyBuilder.Metadata.ClrType == typeof(decimal))
propertyBuilder.HasPrecision(attribute.Precision, attribute.Scale);
return propertyBuilder;
}
///
///
/// /// 精度/// 小数位数public static PropertyBuilder HasPrecision(this PropertyBuilder propertyBuilder, int precision = 18, int scale = 4)
{ //fluntapi方式设置精度
((IInfrastructure)propertyBuilder).Instance.HasPrecision(precision, scale);
return propertyBuilder;
}
public static InternalPropertyBuilder HasPrecision(this InternalPropertyBuilder propertyBuilder, int precision, int scale){
propertyBuilder.Relational(ConfigurationSource.Explicit).HasColumnType($"decimal({precision},{scale})");
return propertyBuilder;
} 以上就是实现的代码，就这么几行。嗯，还是挺简单的.
--------------
以下，则是efcore的源代码。展示了如此之多的可扩展。随着DI的运用和微软的开放，嗯。用烂啦，用炸拉(^_^)
//各种规则和约定
public virtual ConventionSet AddConventions(ConventionSet conventionSet){
ValueGeneratorConvention valueGeneratorConvention = new RelationalValueGeneratorConvention();
ReplaceConvention(conventionSet.BaseEntityTypeChangedConventions, valueGeneratorConvention);
ReplaceConvention(conventionSet.PrimaryKeyChangedConventions, valueGeneratorConvention);
ReplaceConvention(conventionSet.ForeignKeyAddedConventions, valueGeneratorConvention);
ReplaceConvention(conventionSet.ForeignKeyRemovedConventions, valueGeneratorConvention);
var relationalColumnAttributeConvention = new RelationalColumnAttributeConvention();
conventionSet.PropertyAddedConventions.Add(relationalColumnAttributeConvention);
var sharedTableConvention = new SharedTableConvention();
conventionSet.EntityTypeAddedConventions.Add(new RelationalTableAttributeConvention());
conventionSet.EntityTypeAddedConventions.Add(sharedTableConvention);
conventionSet.BaseEntityTypeChangedConventions.Add(new DiscriminatorConvention());
conventionSet.BaseEntityTypeChangedConventions.Add(
new TableNameFromDbSetConvention(Dependencies.Context?.Context, Dependencies.SetFinder));
conventionSet.EntityTypeAnnotationChangedConventions.Add(sharedTableConvention);
conventionSet.PropertyFieldChangedConventions.Add(relationalColumnAttributeConvention);
conventionSet.PropertyAnnotationChangedConventions.Add((RelationalValueGeneratorConvention)valueGeneratorConvention);
conventionSet.ForeignKeyUniquenessChangedConventions.Add(sharedTableConvention);
conventionSet.ForeignKeyOwnershipChangedConventions.Add(sharedTableConvention);
conventionSet.ModelBuiltConventions.Add(new RelationalTypeMappingConvention(Dependencies.TypeMapper));
conventionSet.ModelBuiltConventions.Add(sharedTableConvention);
conventionSet.ModelAnnotationChangedConventions.Add(new RelationalDbFunctionConvention());
return conventionSet;
}//还是各种规则和约定public virtual ConventionSet CreateConventionSet(){
var conventionSet = new ConventionSet();
var propertyDiscoveryConvention = new PropertyDiscoveryConvention(Dependencies.TypeMapper);
var keyDiscoveryConvention = new KeyDiscoveryConvention();
var inversePropertyAttributeConvention = new InversePropertyAttributeConvention(Dependencies.TypeMapper);
var relationshipDiscoveryConvention = new RelationshipDiscoveryConvention(Dependencies.TypeMapper);
conventionSet.EntityTypeAddedConventions.Add(new NotMappedEntityTypeAttributeConvention());
conventionSet.EntityTypeAddedConventions.Add(new NotMappedMemberAttributeConvention());
conventionSet.EntityTypeAddedConventions.Add(new BaseTypeDiscoveryConvention());
conventionSet.EntityTypeAddedConventions.Add(propertyDiscoveryConvention);
conventionSet.EntityTypeAddedConventions.Add(keyDiscoveryConvention);
conventionSet.EntityTypeAddedConventions.Add(inversePropertyAttributeConvention);
conventionSet.EntityTypeAddedConventions.Add(relationshipDiscoveryConvention);
conventionSet.EntityTypeAddedConventions.Add(new DerivedTypeDiscoveryConvention());
conventionSet.EntityTypeIgnoredConventions.Add(inversePropertyAttributeConvention);
var foreignKeyIndexConvention = new ForeignKeyIndexConvention(); var valueGeneratorConvention = new ValueGeneratorConvention();
conventionSet.BaseEntityTypeChangedConventions.Add(propertyDiscoveryConvention);
conventionSet.BaseEntityTypeChangedConventions.Add(keyDiscoveryConvention);
conventionSet.BaseEntityTypeChangedConventions.Add(inversePropertyAttributeConvention);
conventionSet.BaseEntityTypeChangedConventions.Add(relationshipDiscoveryConvention);
conventionSet.BaseEntityTypeChangedConventions.Add(foreignKeyIndexConvention);
conventionSet.BaseEntityTypeChangedConventions.Add(valueGeneratorConvention ); // An ambiguity might have been resolved
conventionSet.EntityTypeMemberIgnoredConventions.Add(inversePropertyAttributeConvention);
conventionSet.EntityTypeMemberIgnoredConventions.Add(relationshipDiscoveryConvention);
var keyAttributeConvention = new KeyAttributeConvention();
var foreignKeyPropertyDiscoveryConvention = new ForeignKeyPropertyDiscoveryConvention();
var backingFieldConvention = new BackingFieldConvention(); var concurrencyCheckAttributeConvention = new ConcurrencyCheckAttributeConvention();
var databaseGeneratedAttributeConvention = new DatabaseGeneratedAttributeConvention();
var requiredPropertyAttributeConvention = new RequiredPropertyAttributeConvention();
var maxLengthAttributeConvention = new MaxLengthAttributeConvention();
var stringLengthAttributeConvention = new StringLengthAttributeConvention();
var timestampAttributeConvention = new TimestampAttributeConvention();
conventionSet.PropertyAddedConventions.Add(backingFieldConvention);
conventionSet.PropertyAddedConventions.Add(concurrencyCheckAttributeConvention);
conventionSet.PropertyAddedConventions.Add(databaseGeneratedAttributeConvention);
conventionSet.PropertyAddedConventions.Add(requiredPropertyAttributeConvention);
conventionSet.PropertyAddedConventions.Add(maxLengthAttributeConvention);
conventionSet.PropertyAddedConventions.Add(stringLengthAttributeConvention);
conventionSet.PropertyAddedConventions.Add(timestampAttributeConvention);
conventionSet.PropertyAddedConventions.Add(keyDiscoveryConvention);
conventionSet.PropertyAddedConventions.Add(foreignKeyPropertyDiscoveryConvention);
conventionSet.PropertyAddedConventions.Add(keyAttributeConvention);
conventionSet.PrimaryKeyChangedConventions.Add(valueGeneratorConvention);
conventionSet.KeyAddedConventions.Add(foreignKeyPropertyDiscoveryConvention);
conventionSet.KeyAddedConventions.Add(foreignKeyIndexConvention);
conventionSet.KeyRemovedConventions.Add(foreignKeyPropertyDiscoveryConvention);
conventionSet.KeyRemovedConventions.Add(foreignKeyIndexConvention);
conventionSet.KeyRemovedConventions.Add(keyDiscoveryConvention);
var cascadeDeleteConvention = new CascadeDeleteConvention();
conventionSet.ForeignKeyAddedConventions.Add(new ForeignKeyAttributeConvention(Dependencies.TypeMapper));
conventionSet.ForeignKeyAddedConventions.Add(foreignKeyPropertyDiscoveryConvention);
conventionSet.ForeignKeyAddedConventions.Add(keyDiscoveryConvention);
conventionSet.ForeignKeyAddedConventions.Add(valueGeneratorConvention );
conventionSet.ForeignKeyAddedConventions.Add(cascadeDeleteConvention);
conventionSet.ForeignKeyAddedConventions.Add(foreignKeyIndexConvention);
conventionSet.ForeignKeyRemovedConventions.Add(keyDiscoveryConvention);
conventionSet.ForeignKeyRemovedConventions.Add(valueGeneratorConvention );
conventionSet.ForeignKeyRemovedConventions.Add(foreignKeyIndexConvention);
conventionSet.ForeignKeyUniquenessChangedConventions.Add(foreignKeyPropertyDiscoveryConvention);
conventionSet.ForeignKeyUniquenessChangedConventions.Add(foreignKeyIndexConvention);
conventionSet.ForeignKeyOwnershipChangedConventions.Add(new NavigationEagerLoadingConvention());
conventionSet.ModelBuiltConventions.Add(new ModelCleanupConvention());
conventionSet.ModelBuiltConventions.Add(keyAttributeConvention);
conventionSet.ModelBuiltConventions.Add(new IgnoredMembersValidationConvention());
conventionSet.ModelBuiltConventions.Add(new PropertyMappingValidationConvention(Dependencies.TypeMapper));
conventionSet.ModelBuiltConventions.Add(new RelationshipValidationConvention());
conventionSet.ModelBuiltConventions.Add(foreignKeyPropertyDiscoveryConvention);
conventionSet.NavigationAddedConventions.Add(backingFieldConvention);
conventionSet.NavigationAddedConventions.Add(new RequiredNavigationAttributeConvention());
conventionSet.NavigationAddedConventions.Add(inversePropertyAttributeConvention);
conventionSet.NavigationAddedConventions.Add(foreignKeyPropertyDiscoveryConvention);
conventionSet.NavigationAddedConventions.Add(relationshipDiscoveryConvention);
conventionSet.NavigationRemovedConventions.Add(relationshipDiscoveryConvention);
conventionSet.IndexAddedConventions.Add(foreignKeyIndexConvention);
conventionSet.IndexRemovedConventions.Add(foreignKeyIndexConvention);
conventionSet.IndexUniquenessChangedConventions.Add(foreignKeyIndexConvention);
conventionSet.PropertyNullabilityChangedConventions.Add(cascadeDeleteConvention);
conventionSet.PrincipalEndChangedConventions.Add(foreignKeyPropertyDiscoveryConvention);
conventionSet.PropertyFieldChangedConventions.Add(keyDiscoveryConvention);
conventionSet.PropertyFieldChangedConventions.Add(foreignKeyPropertyDiscoveryConvention);
conventionSet.PropertyFieldChangedConventions.Add(keyAttributeConvention);
conventionSet.PropertyFieldChangedConventions.Add(concurrencyCheckAttributeConvention);
conventionSet.PropertyFieldChangedConventions.Add(databaseGeneratedAttributeConvention);
conventionSet.PropertyFieldChangedConventions.Add(requiredPropertyAttributeConvention);
conventionSet.PropertyFieldChangedConventions.Add(maxLengthAttributeConvention);
conventionSet.PropertyFieldChangedConventions.Add(stringLengthAttributeConvention);
conventionSet.PropertyFieldChangedConventions.Add(timestampAttributeConvention);
return conventionSet;
}我就是所有的可替换service啦。不要眼花有点多！，找着合适的用起来！
serviceCollection.AsQueryable()
.Where(p => p.ServiceType.ToString().StartsWith("Microsoft.EntityFrameworkCore"))
.Each(sd =>
{
Console.WriteLine($"{sd.Lifetime.ToString().PadRight(15, ' ')}{sd.ServiceType.FullName}");
});原文地址：http://www.cnblogs.com/calvinK/p/7234872.html
.NET社区新闻，深度好文，微信中搜索dotNET跨平台或扫描二维码关注
