How to loop through dbcontext all dbset in Entity Framework Core to get count? - entity-framework-core

Question

I have 20 Dbsets in my context which I want to get the row count for each dbset to make sure all dbset row count is 0. To get the count for one dbset, this is my code:
var person = context.Persons.Count();
Is there a way to loop through the context, get the count for each dbset dynamically?

Answer 1

There is solution. Usage is simple:
var tablesinfo = ctx.GetTablesInfo();
if (tablesinfo != null)
{
var withRecords = tablesinfo
.IgnoreQueryFilters()
.Where(ti => ti.RecordCount > 0)
.ToArray();
}
Extension returns IQueryable<TableInfo> and you can reuse this query later. Probably you will need to filter out Views, but I think you can handle that. Note that IgnoreQueryFilters can be important if you have Global Query Filters defined.
What extension do:
It scans Model for entity types registered for particular DbContext and generates big Concat of Count queries. Here we have to do that via grouping by constant value.
Schematically it will generate the following LINQ query:
var tablesinfo =
ctx.Set<Entity1>.GroupBy(e => 1).Select(g => new TableInfo { TableName = "Entity1", RecordCount = g.Count()})
.Concat(ctx.Set<Entity2>.GroupBy(e => 1).Select(g => new TableInfo { TableName = "Entity2", RecordCount = g.Count()}))
.Concat(ctx.Set<Entity3>.GroupBy(e => 1).Select(g => new TableInfo { TableName = "Entity3", RecordCount = g.Count()}))
...
Which wll be converted to the following SQL:
SELECT "Entity1" AS TableName, COUNT(*) AS RecordCount FROM Entity1
UNION ALL
SELECT "Entity2" AS TableName, COUNT(*) AS RecordCount FROM Entity2
UNION ALL
SELECT "Entity3" AS TableName, COUNT(*) AS RecordCount FROM Entity3
...
Implementation:
public static class QueryableExtensions
{
public class TableInfo
{
public string TableName { get; set; } = null!;
public int RecordCount { get; set; }
}
public static IQueryable<TableInfo> GetTablesInfo(this DbContext ctx)
{
Expression query = null;
IQueryProvider provider = null;
var ctxConst = Expression.Constant(ctx);
var groupingKey = Expression.Constant(1);
// gathering information for MemberInit creation
var newExpression = Expression.New(typeof(TableInfo).GetConstructor(Type.EmptyTypes));
var tableNameProperty = typeof(TableInfo).GetProperty(nameof(TableInfo.TableName));
var recordCountProperty = typeof(TableInfo).GetProperty(nameof(TableInfo.RecordCount));
foreach (var entityType in ctx.Model.GetEntityTypes())
{
var entityParam = Expression.Parameter(entityType.ClrType, "e");
var tableName = entityType.GetTableName();
// ctx.Set<entityType>()
var setQuery = Expression.Call(ctxConst, nameof(DbContext.Set), new[] {entityType.ClrType});
// here we initialize IQueryProvider, which is needed for creating final query
provider ??= ((IQueryable) Expression.Lambda(setQuery).Compile().DynamicInvoke()).Provider;
// grouping paraneter has generic type, we have to specify it
var groupingParameter = Expression.Parameter(typeof(IGrouping<,>).MakeGenericType(typeof(int), entityParam.Type), "g");
// g => new TableInfo { TableName = "tableName", RecordCount = g.Count() }
var selector = Expression.MemberInit(newExpression,
Expression.Bind(tableNameProperty, Expression.Constant(tableName)),
Expression.Bind(recordCountProperty,
Expression.Call(typeof(Enumerable), nameof(Enumerable.Count), new[] {entityParam.Type}, groupingParameter)));
// ctx.Set<entityType>.GroupBy(e => 1)
var groupByCall = Expression.Call(typeof(Queryable), nameof(Queryable.GroupBy), new[]
{
entityParam.Type,
typeof(int)
},
setQuery,
Expression.Lambda(groupingKey, entityParam)
);
// ctx.Set<entityType>.GroupBy(e => 1).Select(g => new TableInfo { TableName = "tableName", RecordCount = g.Count()}))
groupByCall = Expression.Call(typeof(Queryable), nameof(Queryable.Select),
new[] {groupingParameter.Type, typeof(TableInfo)},
groupByCall,
Expression.Lambda(selector, groupingParameter));
// generate Concat if needed
if (query != null)
query = Expression.Call(typeof(Queryable), nameof(Queryable.Concat), new[] {typeof(TableInfo)}, query,
groupByCall);
else
query = groupByCall;
}
// unusual situation, but Model can have no registered entities
if (query == null)
return null;
return provider.CreateQuery<TableInfo>(query);
}
}