Related
I am trying to start using EF6 for a project. My database is already filled with millions of records.
I can't find right explanation how does EF send T-SQL to SQL Server? I am afraid that I am going to download bunch of data to user for no reason.
In code below I have found three way to get my data to List<> but I am not sure which is right way to do WHERE clause at SQL.
I do not want to fill client with millions of record and to query (filter) that data at client.
using (rgtBaza baza = new rgtBaza())
{
var t = baza.Database.SqlQuery<CJE_DOC>("select * from cje_doc where datum between #od and #do",new SqlParameter("od", this.dateTimePickerOD.Value.Date ) ,new SqlParameter("do", this.dateTimePickerOD.Value.Date)).ToList();
var t = baza.CJE_DOC.Where(s => s.DATUM.Value >= this.dateTimePickerOD.Value.Date && s.DATUM.Value <= this.dateTimePickerDO.Value.Date).ToList();
var query = from b in baza.CJE_DOC
where b.DATUM >= this.dateTimePickerOD.Value.Date && b.DATUM.Value <= this.dateTimePickerDO.Value.Date
select b;
var t = query.ToList();
this.dataGridViewCJENICI.DataSource = t;
}
In all 3 cases, the filtering will happen on the database side, the filtering (or WHERE clause) will not take place on the client side.
If you want to verify that this is true, especially for your last 2 options, add some logging so that you can see the generated SQL:
baza.Database.Log = s => Console.WriteLine(s);
In this case, since you are using EF already, choose the 2nd or 3rd options, they are both equivalent with different syntax. Pick your favorite syntax.
In all of those examples, EF6 will generate a SQL query including the where clause - it won't perform the where clause on the client.
It won't actually retrieve any data from the database until you iterate through the results, which in the examples above, is when you call .ToList().
EF6 would only run the filter on the client if you called something like:
baza.CJE_DOC.ToList().Where(x => x.Field == value)
In this instance, it would retrieve the entire table when you called ToList(), and then use a client-side Linq query to filter the results in the where clause.
Any of the 3 will run the query on the SQL Server.
EF relies on LINQ's deferred execution model to build up an expression tree. Once you take an action that causes the expression to be enumerated (e.g. calling ToList(), ToArray(), or any of the other To*() methods), it will convert the expression tree to SQL, send the query to the server, and then start returning the results.
One of the side effects of this is that when using the query or lambda syntax, expressions that EF does not understand how to convert to SQL will cause an exception.
If you absolutely need to use some code that EF can't handle, you can break your code into multiple segments -- filtering things down as far as possible via code that can be converted to SQL, using the AsEnumerable() method to "close off" the EF expression, and doing your remaining filtering or transformations using Linq to Objects.
Simple one really. In SQL, if I want to search a text field for a couple of characters, I can do:
SELECT blah FROM blah WHERE blah LIKE '%text%'
The documentation for App Engine makes no mention of how to achieve this, but surely it's a common enough problem?
BigTable, which is the database back end for App Engine, will scale to millions of records. Due to this, App Engine will not allow you to do any query that will result in a table scan, as performance would be dreadful for a well populated table.
In other words, every query must use an index. This is why you can only do =, > and < queries. (In fact you can also do != but the API does this using a a combination of > and < queries.) This is also why the development environment monitors all the queries you do and automatically adds any missing indexes to your index.yaml file.
There is no way to index for a LIKE query so it's simply not available.
Have a watch of this Google IO session for a much better and more detailed explanation of this.
i'm facing the same problem, but i found something on google app engine pages:
Tip: Query filters do not have an explicit way to match just part of a string value, but you can fake a prefix match using inequality filters:
db.GqlQuery("SELECT * FROM MyModel WHERE prop >= :1 AND prop < :2",
"abc",
u"abc" + u"\ufffd")
This matches every MyModel entity with a string property prop that begins with the characters abc. The unicode string u"\ufffd" represents the largest possible Unicode character. When the property values are sorted in an index, the values that fall in this range are all of the values that begin with the given prefix.
http://code.google.com/appengine/docs/python/datastore/queriesandindexes.html
maybe this could do the trick ;)
Altough App Engine does not support LIKE queries, have a look at the properties ListProperty and StringListProperty. When an equality test is done on these properties, the test will actually be applied on all list members, e.g., list_property = value tests if the value appears anywhere in the list.
Sometimes this feature might be used as a workaround to the lack of LIKE queries. For instance, it makes it possible to do simple text search, as described on this post.
You need to use search service to perform full text search queries similar to SQL LIKE.
Gaelyk provides domain specific language to perform more user friendly search queries. For example following snippet will find first ten books sorted from the latest ones with title containing fern
and the genre exactly matching thriller:
def documents = search.search {
select all from books
sort desc by published, SearchApiLimits.MINIMUM_DATE_VALUE
where title =~ 'fern'
and genre = 'thriller'
limit 10
}
Like is written as Groovy's match operator =~.
It supports functions such as distance(geopoint(lat, lon), location) as well.
App engine launched a general-purpose full text search service in version 1.7.0 that supports the datastore.
Details in the announcement.
More information on how to use this: https://cloud.google.com/appengine/training/fts_intro/lesson2
Have a look at Objectify here , it is like a Datastore access API. There is a FAQ with this question specifically, here is the answer
How do I do a like query (LIKE "foo%")
You can do something like a startWith, or endWith if you reverse the order when stored and searched. You do a range query with the starting value you want, and a value just above the one you want.
String start = "foo";
... = ofy.query(MyEntity.class).filter("field >=", start).filter("field <", start + "\uFFFD");
Just follow here:
init.py#354">http://code.google.com/p/googleappengine/source/browse/trunk/python/google/appengine/ext/search/init.py#354
It works!
class Article(search.SearchableModel):
text = db.TextProperty()
...
article = Article(text=...)
article.save()
To search the full text index, use the SearchableModel.all() method to get an
instance of SearchableModel.Query, which subclasses db.Query. Use its search()
method to provide a search query, in addition to any other filters or sort
orders, e.g.:
query = article.all().search('a search query').filter(...).order(...)
I tested this with GAE Datastore low-level Java API. Me and works perfectly
Query q = new Query(Directorio.class.getSimpleName());
Filter filterNombreGreater = new FilterPredicate("nombre", FilterOperator.GREATER_THAN_OR_EQUAL, query);
Filter filterNombreLess = new FilterPredicate("nombre", FilterOperator.LESS_THAN, query+"\uFFFD");
Filter filterNombre = CompositeFilterOperator.and(filterNombreGreater, filterNombreLess);
q.setFilter(filter);
In general, even though this is an old post, a way to produce a 'LIKE' or 'ILIKE' is to gather all results from a '>=' query, then loop results in python (or Java) for elements containing what you're looking for.
Let's say you want to filter users given a q='luigi'
users = []
qry = self.user_model.query(ndb.OR(self.user_model.name >= q.lower(),self.user_model.email >= q.lower(),self.user_model.username >= q.lower()))
for _qry in qry:
if q.lower() in _qry.name.lower() or q.lower() in _qry.email.lower() or q.lower() in _qry.username.lower():
users.append(_qry)
It is not possible to do a LIKE search on datastore app engine, how ever creating an Arraylist would do the trick if you need to search a word in a string.
#Index
public ArrayList<String> searchName;
and then to search in the index using objectify.
List<Profiles> list1 = ofy().load().type(Profiles.class).filter("searchName =",search).list();
and this will give you a list with all the items that contain the world you did on the search
If the LIKE '%text%' always compares to a word or a few (think permutations) and your data changes slowly (slowly means that it's not prohibitively expensive - both price-wise and performance-wise - to create and updates indexes) then Relation Index Entity (RIE) may be the answer.
Yes, you will have to build additional datastore entity and populate it appropriately. Yes, there are some constraints that you will have to play around (one is 5000 limit on the length of list property in GAE datastore). But the resulting searches are lightning fast.
For details see my RIE with Java and Ojbectify and RIE with Python posts.
"Like" is often uses as a poor-man's substitute for text search. For text search, it is possible to use Whoosh-AppEngine.
from f in CUSTOMERS
where depts.Contains(f.DEPT_ID)
select f.NAME
depts is a list (IEnumerable<int>) of department ids
This query works fine until you pass a large list (say around 3000 dept ids) .. then I get this error:
The incoming tabular data stream (TDS) remote procedure call (RPC) protocol stream is incorrect. Too many parameters were provided in this RPC request. The maximum is 2100.
I changed my query to:
var dept_ids = string.Join(" ", depts.ToStringArray());
from f in CUSTOMERS
where dept_ids.IndexOf(Convert.ToString(f.DEPT_id)) != -1
select f.NAME
using IndexOf() fixed the error but made the query slow. Is there any other way to solve this? thanks so much.
My solution (Guids is a list of ids you would like to filter by):
List<MyTestEntity> result = new List<MyTestEntity>();
for(int i = 0; i < Math.Ceiling((double)Guids.Count / 2000); i++)
{
var nextGuids = Guids.Skip(i * 2000).Take(2000);
result.AddRange(db.Tests.Where(x => nextGuids.Contains(x.Id)));
}
this.DataContext = result;
Why not write the query in sql and attach your entity?
It's been awhile since I worked in Linq, but here goes:
IQuery q = Session.CreateQuery(#"
select *
from customerTable f
where f.DEPT_id in (" + string.Join(",", depts.ToStringArray()) + ")");
q.AttachEntity(CUSTOMER);
Of course, you will need to protect against injection, but that shouldn't be too hard.
You will want to check out the LINQKit project since within there somewhere is a technique for batching up such statements to solve this issue. I believe the idea is to use the PredicateBuilder to break the local collection into smaller chuncks but I haven't reviewed the solution in detail because I've instead been looking for a more natural way to handle this.
Unfortunately it appears from Microsoft's response to my suggestion to fix this behavior that there are no plans set to have this addressed for .NET Framework 4.0 or even subsequent service packs.
https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=475984
UPDATE:
I've opened up some discussion regarding whether this was going to be fixed for LINQ to SQL or the ADO.NET Entity Framework on the MSDN forums. Please see these posts for more information regarding these topics and to see the temporary workaround that I've come up with using XML and a SQL UDF.
I had similar problem, and I got two ways to fix it.
Intersect method
join on IDs
To get values that are NOT in list, I used Except method OR left join.
Update
EntityFramework 6.2 runs the following query successfully:
var employeeIDs = Enumerable.Range(3, 5000);
var orders =
from order in Orders
where employeeIDs.Contains((int)order.EmployeeID)
select order;
Your post was from a while ago, but perhaps someone will benefit from this. Entity Framework does a lot of query caching, every time you send in a different parameter count, that gets added to the cache. Using a "Contains" call will cause SQL to generate a clause like "WHERE x IN (#p1, #p2.... #pn)", and bloat the EF cache.
Recently I looked for a new way to handle this, and I found that you can create an entire table of data as a parameter. Here's how to do it:
First, you'll need to create a custom table type, so run this in SQL Server (in my case I called the custom type "TableId"):
CREATE TYPE [dbo].[TableId] AS TABLE(
Id[int] PRIMARY KEY
)
Then, in C#, you can create a DataTable and load it into a structured parameter that matches the type. You can add as many data rows as you want:
DataTable dt = new DataTable();
dt.Columns.Add("id", typeof(int));
This is an arbitrary list of IDs to search on. You can make the list as large as you want:
dt.Rows.Add(24262);
dt.Rows.Add(24267);
dt.Rows.Add(24264);
Create an SqlParameter using the custom table type and your data table:
SqlParameter tableParameter = new SqlParameter("#id", SqlDbType.Structured);
tableParameter.TypeName = "dbo.TableId";
tableParameter.Value = dt;
Then you can call a bit of SQL from your context that joins your existing table to the values from your table parameter. This will give you all records that match your ID list:
var items = context.Dailies.FromSqlRaw<Dailies>("SELECT * FROM dbo.Dailies d INNER JOIN #id id ON d.Daily_ID = id.id", tableParameter).AsNoTracking().ToList();
You could always partition your list of depts into smaller sets before you pass them as parameters to the IN statement generated by Linq. See here:
Divide a large IEnumerable into smaller IEnumerable of a fix amount of item
I have a basic "property bag" table that stores attributes about my primary table "Card." So when I want to start doing some advanced searching for cards, I can do something like this:
SELECT dbo.Card.Id, dbo.Card.Name
FROM dbo.Card
INNER JOIN dbo.CardProperty ON dbo.CardProperty.IdCrd = dbo.Card.Id
WHERE dbo.CardProperty.IdPrp = 3 AND dbo.CardProperty.Value = 'Fiend'
INTERSECT
SELECT dbo.Card.Id, dbo.Card.Name
FROM dbo.Card
INNER JOIN dbo.CardProperty ON dbo.CardProperty.IdCrd = dbo.Card.Id
WHERE (dbo.CardProperty.IdPrp = 10 AND (dbo.CardProperty.Value = 'Wind' OR dbo.CardProperty.Value = 'Fire'))
What I need to do is to extract this idea into some kind of stored procedure, so that ideally I can pass in a list of property/value combinations and get the results of the search.
Initially this is going to be a "strict" search meaning that the results must match all elements in the query, but I'd also like to have a "loose" query so that it would match any of the results in the query.
I can't quite seem to wrap my head around this one. My previous version of this was to do generate some massive SQL query to execute with a lot of AND/OR clauses in it, but I'm hoping to do something a little more elegant this time. How do I go about doing this?
it seems to me that you have an EAV model here.
if you're using sql server 2005 and up i'd suggest you use XML datatype for this:
http://weblogs.sqlteam.com/mladenp/archive/2006/10/14/14032.aspx
makes searching and stuff much easier with built in xml querying capabilities.
if you can't change your model then look at this:
http://weblogs.sqlteam.com/davidm/articles/12117.aspx
Simple one really. In SQL, if I want to search a text field for a couple of characters, I can do:
SELECT blah FROM blah WHERE blah LIKE '%text%'
The documentation for App Engine makes no mention of how to achieve this, but surely it's a common enough problem?
BigTable, which is the database back end for App Engine, will scale to millions of records. Due to this, App Engine will not allow you to do any query that will result in a table scan, as performance would be dreadful for a well populated table.
In other words, every query must use an index. This is why you can only do =, > and < queries. (In fact you can also do != but the API does this using a a combination of > and < queries.) This is also why the development environment monitors all the queries you do and automatically adds any missing indexes to your index.yaml file.
There is no way to index for a LIKE query so it's simply not available.
Have a watch of this Google IO session for a much better and more detailed explanation of this.
i'm facing the same problem, but i found something on google app engine pages:
Tip: Query filters do not have an explicit way to match just part of a string value, but you can fake a prefix match using inequality filters:
db.GqlQuery("SELECT * FROM MyModel WHERE prop >= :1 AND prop < :2",
"abc",
u"abc" + u"\ufffd")
This matches every MyModel entity with a string property prop that begins with the characters abc. The unicode string u"\ufffd" represents the largest possible Unicode character. When the property values are sorted in an index, the values that fall in this range are all of the values that begin with the given prefix.
http://code.google.com/appengine/docs/python/datastore/queriesandindexes.html
maybe this could do the trick ;)
Altough App Engine does not support LIKE queries, have a look at the properties ListProperty and StringListProperty. When an equality test is done on these properties, the test will actually be applied on all list members, e.g., list_property = value tests if the value appears anywhere in the list.
Sometimes this feature might be used as a workaround to the lack of LIKE queries. For instance, it makes it possible to do simple text search, as described on this post.
You need to use search service to perform full text search queries similar to SQL LIKE.
Gaelyk provides domain specific language to perform more user friendly search queries. For example following snippet will find first ten books sorted from the latest ones with title containing fern
and the genre exactly matching thriller:
def documents = search.search {
select all from books
sort desc by published, SearchApiLimits.MINIMUM_DATE_VALUE
where title =~ 'fern'
and genre = 'thriller'
limit 10
}
Like is written as Groovy's match operator =~.
It supports functions such as distance(geopoint(lat, lon), location) as well.
App engine launched a general-purpose full text search service in version 1.7.0 that supports the datastore.
Details in the announcement.
More information on how to use this: https://cloud.google.com/appengine/training/fts_intro/lesson2
Have a look at Objectify here , it is like a Datastore access API. There is a FAQ with this question specifically, here is the answer
How do I do a like query (LIKE "foo%")
You can do something like a startWith, or endWith if you reverse the order when stored and searched. You do a range query with the starting value you want, and a value just above the one you want.
String start = "foo";
... = ofy.query(MyEntity.class).filter("field >=", start).filter("field <", start + "\uFFFD");
Just follow here:
init.py#354">http://code.google.com/p/googleappengine/source/browse/trunk/python/google/appengine/ext/search/init.py#354
It works!
class Article(search.SearchableModel):
text = db.TextProperty()
...
article = Article(text=...)
article.save()
To search the full text index, use the SearchableModel.all() method to get an
instance of SearchableModel.Query, which subclasses db.Query. Use its search()
method to provide a search query, in addition to any other filters or sort
orders, e.g.:
query = article.all().search('a search query').filter(...).order(...)
I tested this with GAE Datastore low-level Java API. Me and works perfectly
Query q = new Query(Directorio.class.getSimpleName());
Filter filterNombreGreater = new FilterPredicate("nombre", FilterOperator.GREATER_THAN_OR_EQUAL, query);
Filter filterNombreLess = new FilterPredicate("nombre", FilterOperator.LESS_THAN, query+"\uFFFD");
Filter filterNombre = CompositeFilterOperator.and(filterNombreGreater, filterNombreLess);
q.setFilter(filter);
In general, even though this is an old post, a way to produce a 'LIKE' or 'ILIKE' is to gather all results from a '>=' query, then loop results in python (or Java) for elements containing what you're looking for.
Let's say you want to filter users given a q='luigi'
users = []
qry = self.user_model.query(ndb.OR(self.user_model.name >= q.lower(),self.user_model.email >= q.lower(),self.user_model.username >= q.lower()))
for _qry in qry:
if q.lower() in _qry.name.lower() or q.lower() in _qry.email.lower() or q.lower() in _qry.username.lower():
users.append(_qry)
It is not possible to do a LIKE search on datastore app engine, how ever creating an Arraylist would do the trick if you need to search a word in a string.
#Index
public ArrayList<String> searchName;
and then to search in the index using objectify.
List<Profiles> list1 = ofy().load().type(Profiles.class).filter("searchName =",search).list();
and this will give you a list with all the items that contain the world you did on the search
If the LIKE '%text%' always compares to a word or a few (think permutations) and your data changes slowly (slowly means that it's not prohibitively expensive - both price-wise and performance-wise - to create and updates indexes) then Relation Index Entity (RIE) may be the answer.
Yes, you will have to build additional datastore entity and populate it appropriately. Yes, there are some constraints that you will have to play around (one is 5000 limit on the length of list property in GAE datastore). But the resulting searches are lightning fast.
For details see my RIE with Java and Ojbectify and RIE with Python posts.
"Like" is often uses as a poor-man's substitute for text search. For text search, it is possible to use Whoosh-AppEngine.