Important

2021-11-16 About 1 min

# Version

ShardingCore version is a.b.c.d

a:EFCore version
b:ShardingCore version
c:ShardingCore second version
d:ShardingCore fix version

# Common Problem

current dbcontext is virtual dbcontext not real execute dbcontext，real dbcontext is in DbContextExecutor

# DbContext Constructor Problem

dont use ant method that will created model before.

        public DefaultShardingDbContext(DbContextOptions<DefaultShardingDbContext> options) : base(options)
        {
            //dont invoke
            //ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;
            //Database.SetCommandTimeout(30000);
        }

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# Performance loss

query no sharding entity,ShardingCore slow than EFCore 0.005ms single query;

# Disadvantage

use more conection in single query，but u can limit with start up options:MaxQueryConnectionsLimit
sharding entity not support include,if u want join two entities u can use join.
sharding entity dont set nav properties like icollection or list

# GetHashCode

c# GetHashCode

When we do not modify the object, we call hashcode many times to return the same integer. In the same application, if we execute it many times, the integer returned by each execution may be inconsistent suggestion use sharding-core provider method ShardingCoreHelper.GetStringHashCode(shardingKeyStr)

# Group By

if use group by queryable will append order by while order by item is empty,if has order by item shoule use full select properties

# GUID

c# guid compare is difference with sqlserver uniqueidentifier，sharding-core is fix this bug,use SqlGuid to compare,but not fix Nullable<Guid> if u want fix it. example:

/// <summary>
/// like this example
/// </summary>
/// <typeparam name="TShardingDbContext"></typeparam>
public class SqlServerNullableGuidCSharpLanguageShardingComparer<TShardingDbContext>:CSharpLanguageShardingComparer<TShardingDbContext> where TShardingDbContext : DbContext, IShardingDbContext
{
        public override int Compare(IComparable x, IComparable y, bool asc)
        {
            if (x is XXType xg && y is XXType yg)
            {
                return new XXFixedType(xg).SafeCompareToWith(new XXFixedType(yg), asc);
            }
            return base.Compare(x, y, asc);
        }
}

//configure
.ReplaceShardingComparer(sp=>new SqlServerNullableGuidCSharpLanguageShardingComparer<DefaultShardingDbContext>())

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注意:fix c# compare guid

# auto increment field

do not configure auto increment field in sharding-core sharding field。e.g:increment id

# EnsureCreated

DbContext.Database.EnsureCreated() if u want use this method ,plz impl IMigrationsSqlGenerator

# sharding with time

if u use sharding with time field,plz readpagination

Introduce