Git information is in a separate document.
Databases that you should need for development:
Even though our test run will run modifications to the test databases, don't check in these *.mdb
and *.db
files with your commit, to avoid bad merge-cases.
We use Fake and Paket. You have to run build.cmd
on Windows (or sh ./build.sh
on Mac/Linux) before opening the solutions.
The main source solution is SQLProvider.sln
.
The unit tests are located in another one, SQLProvider.Tests.sln
, and when you open the solution, it will lock the bin\net472\FSharp.Data.SqlProvider.dll
, and after that you can't build the main solution.
*.html
help files by the build-script.src/ProvidedTypes.fsi
, src/ProvidedTypes.fs
and src/Code/ExpressionOptimizer.fs
are coming from other repositoried restored by first build. Location is at packet.dependencies. Don't edit them manually.There are database specific test files as scripts in the test solution, /tests/SqlProvider.Tests/scripts/, but also one generic /tests/SqlProvider.Tests/QueryTests.fs which is running all the SQLite tests in the build script.
You have a source code like:
type sql = SqlDataProvider<...params...>
let dc = sql.GetDataContext()
What will first happen in the design-time, is that this will call createTypes
of SqlDesignTime.fs and create (as lazily as possible) the database schema types (the shape of the database). These methods are added to the sql.datacontext
and are stored to concurrent dictionaries. Visual Studio will do a lot of background processing so thread-safety is important here.
GetDataContext()
will return a dynamic class called dataContext which will on design-time call class SqlDataContext in file SqlRuntime.DataContext.fs through interface ISqlDataContext
. SqlDataContext uses ProviderBuilder to create database specific providers, fairly well documented ISqlProvider
in file SqlRuntime.Common.fs.
The entity-items themselves are rows in the database data and they are modelled as dynamic sub-classes of SqlEntity
, base-class in file SqlRuntime.Common.fs which can be basically think of as wrapper for Dictionary<string,obj>
(a column name, and the value). SqlEntity is used for all-kind of result-data actually, so the data columns may not correspond to the actual data values. Mostly the results of the data are shaped as SqlQueryable<SqlEntity>
, or SqlQueryable<'T>
which is a SQLProvider's class for IQueryable<'T>
items.
query {
for cust in dbc.Main.Customers do
where ("ALFKI" = cust.CustomerId)
select cust
} |> Seq.toArray
This query is translated to a LINQ-expression-tree through Microsoft.FSharp.Linq.QueryFSharpBuilder. That will call IQueryable<'T>
's member Provider to execute two things for the LINQ-expression-tree: first CreateQuery
and later Execute
.
CreateQuery
will hit our SqlQueryable<...>
's Provider (IQueryProvider) property. LINQ-expression-trees can be kind of recursive type structures, so we it will call CreateQuery for each linq-method. We get the expression-tree as parameter, and parse that with (multi-layer-) active patterns.
Our example the LINQ-expression tree is:
|
so it would hit this in SqlRuntime.Linq.fs:
| MethodCall(None, (MethodWithName "Where" as meth), [ SourceWithQueryData source; OptionalQuote qual ]) ->
because the LINQ-expression-tree has ExpressionType.Call
named "Where" with source of IWithSqlService (which is the SqlQueryableCondition
). If the conditions are having SqlColumnGet
s, a pattern that says that it's SqlEntity
with method GetColumn
, we know that it has to be part of SQL-clause.
We collect all the known patterns to IWithSqlService
s field SqlExpression, being a type SqlExp
, our non-complete known recursive model-tree of SQL clauses.
Eventually there also comes the call executeQuery
(or executeQueryScalar
for SQL-queries that will return a single value like count), either by enumeration of our IQueryable or at the end of LINQ-expression-tree. That will call QueryExpressionTransformer.convertExpression
. What happens there (in
SqlRuntime.Linq.fs):
SqlExp
to real SQL-clause with QueryExpressionTransformer.convertExpression
calling provider's GenerateQueryText
-method. Each provider may have some differences in their SQL-syntax.IEnumerable<SqlEntity>
(or a single return value like count).In our example the whole cust object was selected.
For security reasons we don't do SELECT *
but we actually list the columns that are there at compile time.
The TupleIndex
of IWithSqlService is a way to collect joined tables to match the sql-aliasses, here the [cust]
.
|
Now, if the select-clause would have been complex:
query {
for emp in dc.Main.Employees do
select (emp.BirthDate.DayOfYear + 3)
} |> Seq.toArray
We don't know the function of DayOfYear for each different SQL-providers (Oracle/MSSQL/Odbc/...), but we still want tihs code to work. The LINQ-expression-tree for this query is:
|
What happens now, is that in SqlRuntime.QueryExpression.fs we parse the whole LINQ-expression-tree, and find the parts that we do know to belong to SQL:
the SqlEntity's emp.GetColumn("BirthDate")
, and create a lambda-expression where this is replaced with a parameter:
fun empBirthDate -> empBirthDate.DayOfYear + 3
Now when we get the empBirthDate from the SQL result, we can execute this lambda for the parameter, in .NET-side, not SQL, and then we get the correct result. This is done with for e in results -> projector.DynamicInvoke(e)
in SqlRuntime.Linq.fs.
If you do IN-query (LINQ-Contains) to IEnumerable, it's as normal IN-query, but if the source collection is SqlQueryable
This documentation was written on 2017-04-11.