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JordanMarr / SqlHydra

SqlHydra is a suite of NuGet packages for working with databases in F# including code generation tools and query expressions.
MIT License
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fsharp orm typeprovider

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SqlHydra

SqlHydra is a set of NuGet packages for working with databases in F# with an emphasis on type safety and convenience.

SqlHydra.Cli

SqlHydra.Cli is a dotnet tool that generates F# types and readers for SQL Server, PostgreSQL, Oracle and SQLite databases.

SqlHydra.Query

SqlHydra.Query provides strongly typed Linq queries against generated types.

Notes

Contributors ✨

Thanks goes to these wonderful people:


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This project follows the all-contributors specification. Contributions of any kind welcome!

Contributing

SqlHydra.Cli NuGet version (SqlHydra.Cli)

Local Install (recommended)

Run the following commands from your project directory: 1) dotnet new tool-manifest 2) dotnet tool install SqlHydra.Cli

Configure and Run

Run the tool from the command line, passing in a database provider: mssql, npgsql, sqlite, oracle

dotnet sqlhydra mssql

TOML Creation Wizard

The wizard will prompt you for the following input:

- Enter a database Connection String:

This is the connection string that SqlHydra can use to query table and column metadata.

- Enter an Output Filename (Ex: AdventureWorks.fs):

This is the filename that your generated types will be added to. (This file will be automatically added to your fsproj.)

- Enter a Namespace (Ex: MyApp.AdventureWorks):

This is the namespace that your generated table record types will be created in.

- Select a use case:

> SqlHydra.Query integration (default)
  Other data library
  Standalone

Selecting a use case will set the base configuration options in your TOML file.

For more details, see the .toml configuration.

Build Event (optional)

To regenerate after a Rebuild (only when in Debug mode), you can run SqlHydra from an fsproj build event:

  <!-- Regenerate entities on Rebuild in Debug mode -->
  <Target Name="SqlHydra" BeforeTargets="Clean" Condition="'$(Configuration)' == 'Debug'">
    <Exec Command="dotnet sqlhydra mssql" />
  </Target>

Support for Postgres Enums

Postgres enum types are generated as CLR enums! You will, however, still need to manually "register" your custom enums.

If using Npgsql v7 or later:

// Global mapping should occur only once at startup:
// `experiments.mood` is the generated enum, and "experiments.mood" is the "{schema}.{enum}".
let dataSourceBuilder = NpgsqlDataSourceBuilder(DB.connectionString)
dataSourceBuilder.MapEnum<ext.mood>("ext.mood") |> ignore

If using Npgsql v6 or earlier:

// Global mapping should occur only once at startup:
// `experiments.mood` is the generated enum, and "experiments.mood" is the "{schema}.{enum}".
Npgsql.NpgsqlConnection.GlobalTypeMapper.MapEnum<experiments.mood>(nameof experiments.mood) |> ignore

💥 Npgsql v8.0.0 fails when inserting an enum.

Support for Postgres Arrays

SqlHydra.Cli supports text[] and integer[] column types.

Sqlite Data Type Aliases

Sqlite stores all data as either an INTEGER, REAL, TEXT or BLOB type. Fortunately, you can also use aliases for data types more commonly used in other databases in your table definitions and Sqlite will translate them to the appropriate type. Using these type aliases also allows SqlHydra.Cli to generate the desired .NET CLR property type.

Here is a list of valid data type aliases (or "affinity names"): https://www.sqlite.org/datatype3.html#affinity_name_examples

SQL Server Troubleshooting

The following exception may occur with the latest version of Microsoft.Data.SqlClient:

Microsoft.Data.SqlClient.SqlException (0x80131904): 
A connection was successfully established with the server, but then an error occurred during the login process. 
(provider: SSL Provider, error: 0 - The certificate chain was issued by an authority that is not trusted.)

The most simple way to resolve this is to append ;TrustServerCertificate=True to the connection string in your .toml configuration file. UPDATE: This behavior has been fixed in Microsoft.Data.SqlClient v4.1.1.

Generated Table Types for AdventureWorks

// This code was generated by SqlHydra.SqlServer.
namespace SampleApp.AdventureWorks

module dbo =
    type ErrorLog =
        { ErrorLogID: int
          ErrorTime: System.DateTime
          UserName: string
          ErrorNumber: int
          ErrorMessage: string
          ErrorSeverity: Option<int>
          ErrorState: Option<int>
          ErrorProcedure: Option<string>
          ErrorLine: Option<int> }

    let ErrorLog = table<ErrorLog>

    type BuildVersion =
        { SystemInformationID: byte
          ``Database Version``: string
          VersionDate: System.DateTime
          ModifiedDate: System.DateTime }

    let BuildVersion = table<BuildVersion>

module SalesLT =
    type Address =
        { City: string
          StateProvince: string
          CountryRegion: string
          PostalCode: string
          rowguid: System.Guid
          ModifiedDate: System.DateTime
          AddressID: int
          AddressLine1: string
          AddressLine2: Option<string> }

    let Address = table<Address>

    type Customer =
        { LastName: string
          PasswordHash: string
          PasswordSalt: string
          rowguid: System.Guid
          ModifiedDate: System.DateTime
          CustomerID: int
          NameStyle: bool
          FirstName: string
          MiddleName: Option<string>
          Title: Option<string>
          Suffix: Option<string>
          CompanyName: Option<string>
          SalesPerson: Option<string>
          EmailAddress: Option<string>
          Phone: Option<string> }

    let Customer = table<Customer>

    // etc...

Strongly Typed Data Readers

The generated HydraReader class works in tandem with SqlHydra.Query for reading queried entities, but it can also be used on its own with any query library that returns an IDataReader.

TOML Configuration Reference

Generating Multiple TOML Files

It is also possible to have more than one .toml file in the same project. By default, SqlHydra will create a .toml file named after the version of SqlHydra used. For example, running dotnet sqlhydra sqlite will generate sqlhydra-sqlite.toml.

However, you can also specify a name for your .toml file: dotnet sqlhydra sqlite -t "shared.toml" This can be useful for various use cases, such as:

Supported Frameworks

.NET 6 - .NET 8 are currently supported. (If you still need support for .NET 5, use the deprecated SqlHydra.SqlServer, SqlHydra.Sqlite, SqlHydra.Npgsql or SqlHydra.Oracle tools.)

.NET 6 and Greater

The new .NET 6 System.DateOnly and System.TimeOnly types are now supported by all generators.

SqlHydra.Query NuGet version (SqlHydra.Query)

SqlHydra.Query wraps the powerful SqlKata query generator with F# computation expression builders for strongly typed query generation. SqlHydra.Query can be used with any library that accepts a data reader; however, is designed pair well with SqlHydra generated records and readers!

Creating a Query Context

/// Opens a connection and creates a QueryContext that will generate SQL Server dialect queries
let openContext() = 
    let compiler = SqlKata.Compilers.SqlServerCompiler()
    let conn = new SqlConnection("Replace with your connection string")
    conn.Open()
    let ctx = new QueryContext(conn, compiler)
    #if DEBUG
    // Writes your queries and parameters to the console
    ctx.Logger <- printfn "SQL: %O" 
    #endif
    ctx

Select Builders

There are two main select builders that you can use to create queries:

let getErrorNumbers () =
    selectTask HydraReader.Read openContext {
        for e in dbo.ErrorLog do
        select e.ErrorNumber
    }

Input: 1) You must pass in the HydraReader.Read static method to be passed in (which is generated by SqlHydra.Cli when the "Generate HydraReader?" option is selected). 2) You must pass in either an existing QueryContext or a function that will create a new one.

Example 1: Creating a new QueryContext

In this case, the selectAsync expression will create the QueryContext using the given openContext function, and it will also dispose it for you automatically.

let openContext() = 
    let compiler = SqlKata.Compilers.SqlServerCompiler()
    let conn = new SqlConnection("Replace with your connection string")
    conn.Open()
    new QueryContext(conn, compiler)

let getErrorNumbers () =
    selectAsync HydraReader.Read openContext {
        for e in dbo.ErrorLog do
        select e.ErrorNumber
    }

Example 2: Sharing a QueryContext

In this case, you manually create a shared QueryContext and pass it to each selectTask expression. You are also responsible for disposing the QueryContext manually.

let getUserOrders email =
    task {
        use ctx = openContext ()

        let! userInfo = 
            selectTask HydraReader.Read ctx {
                for user in dbo.Users do
                where (user.Email = email)
            }

        let! orderHeaders = 
            selectTask HydraReader.Read ctx {
                for o in dbo.OrderHeaders do
                where (o.CustomerEmail = email)
            }

        return { User = userInfo; Orders = orderHeaders }
    }

Notes on Select Builders

Creating a Custom selectAsync or selectTask Builder

If the redundancy of passing the generated HydraReader.Read static method into the selectAsync and selectTask builders bothers you, you can easily create your builder that has it baked-in:

let selectTask' ct = selectTask HydraReader.Read ct

// Usage:
let! distinctCustomerNames = 
    selectTask' openContext {
        for c in SalesLT.Customer do
        select (c.FirstName, c.LastName)
        distinct
    }

Selecting city and state columns only:

let getCities (cityFilter: string) = 
    selectTask HydraReader.Read openContext {
        for a in SalesLT.Address do                             // Specifies a FROM table in the query
        where (a.City = cityFilter)                             // Specifies a WHERE clause in the query
        select (a.City, a.StateProvince) into selected          // Specifies which entities and/or columns to SELECT in the query
        mapList (                                               // Transforms the query results
            let city, state = selected
            $"City, State: %s{city}, %s{state}"
        )
    }

Special where filter operators:

Select Address entities where City starts with S:

let getAddressesInCitiesStartingWithS () = 
    selectAsync HydraReader.Read openContext {
        for a in SalesLT.Address do
        where (a.City =% "S%")
        select a
    }

NOTE: You should always explicitly select the table or tables. As of v2.5.0, selecting the table(s) will explicitly select all columns in the table. Otherwise, it will issue a SELECT * query which is slightly less performant as it will require a table scan.

Try to select a single row (this example returns a decimal option):

let tryGetOrderTotal (orderId: int) = 
        selectAsync HydraReader.Read openContext {
            for o in SalesLT.Order do
            where (o.Id = orderId)
            select o.Total
            tryHead
        }

Joins

Select top 10 Product entities with inner joined category name:

let getProductsWithCategory () = 
    selectTask HydraReader.Read openContext {
        for p in SalesLT.Product do
        join c in categoryTable on (p.ProductCategoryID.Value = c.ProductCategoryID)
        select (p, c.Name)
        take 10
    }

[!WARNING] You need to write the join on equality condition using the known (left) table variable on the left and the new (right) one on the right; otherwise, the F# compiler will complain that p and c are not defined. (This order condition is due to the way F# Query Expressions are defined.)

Select Customer with left joined Address where CustomerID is in a list of values: (Note that left joined tables will be of type 'T option, so you will need to use the .Value property to access join columns.)

let getCustomerAddressesInIds (customerIds: int list) =
    selectAsync HydraReader.Read openContext) {
        for c in SalesLT.Customer do
        leftJoin ca in SalesLT.CustomerAddress on (c.CustomerID = ca.Value.CustomerID)
        leftJoin a  in SalesLT.Address on (ca.Value.AddressID = a.Value.AddressID)
        where (c.CustomerID |=| customerIds)
        orderBy c.CustomerID
        select (c, a)
    }

When selecting individual columns from a left joined table, you can force non-optional columns to be optional by wrapping them in Some:

let getCustomerZipCodes (customerId: int) =
    selectAsync HydraReader.Read openContext {
        for c in SalesLT.Customer do
        leftJoin ca in SalesLT.CustomerAddress on (c.CustomerID = ca.Value.CustomerID)
        leftJoin a  in SalesLT.Address on (ca.Value.AddressID = a.Value.AddressID)
        where (c.CustomerID = customerId)
        orderBy c.CustomerID
        select (c, Some a.Value.ZipCode)
    }

To create a join query with multi-columns, use tuples:

select {
    for o in SalesLT.OrderHeaders do
    join d in SalesLT.OrderDetails on ((o.SalesOrderID, o.ModifiedDate) = (d.SalesOrderID, d.ModifiedDate))
    select (o, d)
}

[!WARNING] The join on clause only supports simple column = column comparisons. Constant value parameters are not supported. Any custom filters that you might normally put in the on clause, especially those involving input parameters, will need to be moved to the where clause. This is because the F# join on syntax does not support complex filter clauses.

Transforming Query Results

To transform the query results use the mapSeq, mapArray or mapList operations. 

    let! lineTotals =
        selectTask HydraReader.Read openContext {
            for o in SalesLT.OrderHeaders do
            join d in SalesLT.OrderDetails on (o.SalesOrderID = d.SalesOrderID)
            where (o.OnlineOrderFlag = true)
            select (o, d) into selected
            mapList (
                let o,d = selected
                {| 
                    ShipDate = 
                        match o.ShipDate with
                        | Some d -> d.ToShortDateString()
                        | None -> "No Order Number"
                    LineTotal = (decimal qty) * unitPrice
                |}
            )
        }

If a custom subset of entities and/or columns has been selected in the query, you will need to project them into a new binding using the into operation:

    let! lineTotals =
        selectTask HydraReader.Read openContext {
            for o in SalesLT.OrderHeaders do
            join d in SalesLT.OrderDetails on (o.SalesOrderID = d.SalesOrderID)
            where (o.OnlineOrderFlag = true)
            select (o, d.OrderQty, d.UnitPrice) into selected  // project selected values so they can be mapped
            mapList (
                let o, qty, unitPrice = selected               // unpack the selected values for use in transform
                {| 
                    ShipDate = 
                        match o.ShipDate with
                        | Some d -> d.ToShortDateString()
                        | None -> "No Order Number"
                    LineTotal = (decimal qty) * unitPrice
                |}
            )
        }

You can also use mapSeq in conjunction with tryHead to map a single result:

        selectAsync HydraReader.Read openContext {
            for o in SalesLT.Order do
            where (o.Id = orderId)
            select o.Total
            mapSeq {| GrandTotal = o.Total |}
            tryHead
        }

Aggregates

Aggregate functions (can be used in select, having and orderBy clauses):

/// Select categories with an avg product price > 500 and < 1000
let getCategoriesWithHighAvgPrice () = 
    selectTask HydraReader.Read openContext {
        for p in SalesLT.Product do
        where (p.ProductCategoryID <> None)
        groupBy p.ProductCategoryID
        having (minBy p.ListPrice > 500M && maxBy p.ListPrice < 1000M)
        select (p.ProductCategoryID, minBy p.ListPrice, maxBy p.ListPrice) into selected
        mapList (
            let catId, minPrice, maxPrice = selected
            $"CatID: {catId}, MinPrice: {minPrice}, MaxPrice: {maxPrice}"
        )
    }

Alternative Row Count Query:

let! customersWithNoSalesPersonCount =
    selectTask HydraReader.Read openContext {
        for c in SalesLT.Customer do
        where (c.SalesPerson = None)
        count
    }

[!WARNING] In some cases when selecting an aggregate of a non-NULL column, the database will still return NULL if the query result set is empty, for example if selecting the MAX of an INT column in an empty table. This is not supported and will throw an exception. If your query might return NULL for the aggregate of a non-NULL column, you may include Some in the aggregate to support parsing the NULL as an Option value:

❌ INCORRECT:

/// Select the minimum item price above a threshold
let getNextLowestPrice threshold = 
    selectTask HydraReader.Read openContext {
        for p in SalesLT.Product do
        where (p.ListPrice > threshold)
        select (minBy p.ListPrice)
    }

✅ CORRECT:

/// Select the minimum item price above a threshold
let getNextLowestPrice threshold = 
    selectTask HydraReader.Read openContext {
        for p in SalesLT.Product do
        where (p.ListPrice > threshold)
        select (minBy (Some p.ListPrice))
    }

WHERE Subqueries

Use the subqueryMany function for subqueries that return multiple rows for comparison:

// Create a subquery that gets top 5 avg prices by category ID:
let top5CategoryIdsWithHighestAvgPrices = 
    select {
        for p in SalesLT.Product do
        where (p.ProductCategoryID <> None)
        groupBy p.ProductCategoryID
        orderByDescending (avgBy p.ListPrice)
        select p.ProductCategoryID
        take 5
    }

// Get category names where the category ID is "IN" the subquery:
let! top5Categories =
    selectTask HydraReader.Read openContext {
        for c in SalesLT.ProductCategory do
        where (Some c.ProductCategoryID |=| subqueryMany top5CategoryIdsWithHighestAvgPrices)
        select c.Name
    }

Use the subqueryOne function for subqueries that return a single value for comparison:

// Create a subquery that gets the avg list price (a single value):
let avgListPrice = 
    select {
        for p in SalesLT.Product do
        select (avgBy p.ListPrice)
    } 

// Get products with a price > the average price
let! productsWithAboveAveragePrice =
    selectTask HydraReader.Read openContext {
        for p in SalesLT.Product do
        where (p.ListPrice > subqueryOne avgListPrice)
        select (p.Name, p.ListPrice)
    }
Correlated Subqueries

If the subquery is correlated with the parent query (i.e., the subquery references a row variable from the parent query), use the correlate keyword in the subquery to introduce the correlated variable. Note: the variable name in the subquery must match the variable name in the parent query, because it determines the table alias in the generated SQL query.

// Create a subquery that gets the min price for this product line,
// referencing a row variable "outer" from the parent query:
let lowestPriceByProductLine = 
    select {
        for inner in Production.Product do
        correlate outer in Production.Product
        where (inner.ProductLine = outer.ProductLine)
        select (minBy inner.ListPrice)
    }

// Get the products whose price is the lowest of all prices in its product line.
// The name "outer" needs to match the subquery.
let! cheapestByProductLine = 
    selectTask HydraReader.Read openContext {
        for outer in Production.Product do
        where (outer.ListPrice = subqueryOne lowestPriceByProductLine)
        select (outer.Name, outer.ListPrice)
    }

Distinct Query:

let! distinctCustomerNames = 
    selectTask HydraReader.Read openContext {
        for c in SalesLT.Customer do
        select (c.FirstName, c.LastName)
        distinct
    }

Dos and Don'ts

:boom: The select clause only supports tables and fields for the sake of modifying the generated SQL query and the returned query type 'T. Transformations (i.e. .ToString() or calling any functions is not supported and will throw an exception.

:boom: The where clause will automatically parameterize your input values. However, similar to the select clause, the where clause does not support calling an transformations (i.e. .ToString()). So you must prepare any parameter transformations before the builder.

✅ CORRECT:

let getCities () =
    let city = getCity() // DO prepare where parameters above and then pass into the where clause
    selectTask HydraReader.Read openContext {
        for a in SalesLT.Address do
        where (a.City = city)
        select (a.City, a.StateProvince) into (city, state)
        mapList $"City: %s{city}, State: %s{state}"   // DO transforms using the `mapSeq`, `mapArray` or `mapList` operations
    }

❌ INCORRECT:

let getCities () =
    selectTask HydraReader.Read openContext {
        for a in SalesLT.Address do
        where (a.City = getCity()) // DO NOT perform calculations or translations within the builder
        select ($"City: %s{city}, State: %s{state}")   // DO NOT transform results within the builder 
    }

Insert Builder

Simple Inserts

For simple inserts with no identity column and no included/excluded columns, use the into _ syntax:

let! rowsInserted = 
    insertTask openContext {
        into Person.Person
        entity 
            {
                dbo.Person.ID = Guid.NewGuid()
                dbo.Person.FirstName = "Bojack"
                dbo.Person.LastName = "Horseman"
                dbo.Person.LastUpdated = DateTime.Now
            }
    }

printfn "Rows inserted: %i" rowsInserted

Insert with an Identity Field

If you have an Identity column or if you want to specify columns to include/exclude, use the for _ in _ do syntax. By default, all record fields will be included as insert values, so when using an identity column, you must handle it in one of two ways: 1) Mark it with getId. This will prevent it from being added as an insert value, and it will also select and return the identity field. 2) Mark it with excludeColumn to prevent it from being added as an insert value.


let! errorLogID =
    insertTask openContext {
        for e in dbo.ErrorLog do
        entity 
            {
                dbo.ErrorLog.ErrorLogID = 0 // Adding `getId` below will ignore this value.
                dbo.ErrorLog.ErrorTime = System.DateTime.Now
                dbo.ErrorLog.ErrorLine = None
                dbo.ErrorLog.ErrorMessage = "TEST"
                dbo.ErrorLog.ErrorNumber = 400
                dbo.ErrorLog.ErrorProcedure = (Some "Procedure 400")
                dbo.ErrorLog.ErrorSeverity = None
                dbo.ErrorLog.ErrorState = None
                dbo.ErrorLog.UserName = "jmarr"
            }
        getId e.ErrorLogID
    }

printfn "ErrorLogID Identity: %i" errorLogID

Multiple Inserts

To insert multiple entities in one query, use the entities operation in conjunction with the AtLeastOne type to ensure that at least one item exists in the collection. (The AtLeastOne forces you to handle the case where an empty collection is passed to entities which would throw a runtime exception.)

NOTE: getId is not supported for multiple inserts with entities! So if you are inserting multiple entities that have an identity field, you must use excludeColumn on the identity column.

let currenciesMaybe = 
    [ 0..2 ] 
    |> List.map (fun i -> 
        {
            Sales.Currency.CurrencyCode = $"BC{i}"
            Sales.Currency.Name = "BitCoin"
            Sales.Currency.ModifiedDate = System.DateTime.Now
        }
    )
    |> AtLeastOne.tryCreate

match currenciesMaybe with
| Some currencies ->
    do! insertTask openContext {
            into Sales.Currency
            entities currencies
        } :> Task // upcast to Task if you want to ignore the resulting value
| None ->
    printfn "Skipping insert because entities seq was empty."

Upsert

Upsert support has been added for Postgres and Sqlite only because they support ON CONFLICT DO ___ which provides atomic upsert capabilities. (Unfortunately, SQL Server and Oracle only have MERGE which can suffer from concurrency issues. For SQL Server bulk operations, please try my SqlBulkTools.Fsharp library.)

Postgres: open SqlHydra.Query.NpgsqlExtensions

Sqlite: open SqlHydra.Query.SqliteExtensions

Example Usage:

    /// Inserts an address or updates it if it already exists.
    let upsertAddress address = 
        insertTask openContext {
            for a in Person.Address do
            entity address
            onConflictDoUpdate a.AddressID (
                a.AddressLine1,
                a.AddressLine2,
                a.City,
                a.StateProvince,
                a.CountryRegion,
                a.PostalCode,
                a.ModifiedDate
            )
        }

Or, if you have multiple addresses to upsert:

    /// Inserts multiple addresses or updates them if they already exist.
    let upsertAddress addresses =
        match addresses |> AtLeastOne.tryCreate with
        | Some addresses -> 
            insertTask openContext {
                for a in Person.Address do
                entities addresses
                onConflictDoUpdate a.AddressID (
                    a.AddressLine1,
                    a.AddressLine2,
                    a.City,
                    a.StateProvince,
                    a.CountryRegion,
                    a.PostalCode,
                    a.ModifiedDate
                )
            }
        | None ->
            printfn "No addresses to insert."
            0
    /// Tries to insert an address if it doesn't already exist.
    let tryInsertAddress address = 
        insertTask openContext {
            for a in Person.Address do
            entity address
            onConflictDoNothing a.AddressID
        }

Update Builder

Update Individual Fields

To update individual columns, use the set operation.

do! updateAsync openContext {
        for e in dbo.ErrorLog do
        set e.ErrorNumber 123
        set e.ErrorMessage "ERROR #123"
        set e.ErrorLine (Some 999)
        set e.ErrorProcedure None
        where (e.ErrorLogID = 1)
    } :> Task // upcast to Task if you want to ignore the resulting value

Update Entire Record

To update an entire record, use the entity operation. You may optionally use includeColumn to specify an allow list of one or more columns on the record to include in the update. You may optionally use excludeColum to specify a deny list of one or more columns on the record to exclude from the update. NOTE: You may use includeColumn or excludeColumn multiple times - once for each column to include/exclude.

let! rowsUpdated = 
    updateTask openContext {
        for e in dbo.ErrorLog do
        entity 
            {
                dbo.ErrorLog.ErrorLogID = 0 // Add `excludeColumn` below to ignore an identity column
                dbo.ErrorLog.ErrorTime = System.DateTime.Now
                dbo.ErrorLog.ErrorLine = None
                dbo.ErrorLog.ErrorMessage = "TEST"
                dbo.ErrorLog.ErrorNumber = 400
                dbo.ErrorLog.ErrorProcedure = (Some "Procedure 400")
                dbo.ErrorLog.ErrorSeverity = None
                dbo.ErrorLog.ErrorState = None
                dbo.ErrorLog.UserName = "jmarr"
            }
        excludeColumn e.ErrorLogID // Exclude the identity column
        where (e.ErrorLogID = errorLog.ErrorLogID)
    }

If you want to apply an update to all records in a table, you must use the updateAll keyword or else it will throw an exception (it's a safety precaution that may save you some trouble. 😊):

update {
    for c in Sales.Customer do
    set c.AccountNumber "123"
    updateAll
}

Delete Builder

do! deleteTask openContext {
        for e in dbo.ErrorLog do
        where (e.ErrorLogID = 5)
    } :> Task // upcast to Task if you want to ignore the resulting value

If you want to delete all records in a table, you must use the deleteAll keyword in lieu of a where statement or else it will not compile:

let! rowsDeleted = 
    deleteTask openContext {
        for c in Sales.Customer do
        deleteAll
    }

printfn "Rows deleted: %i" rowsDeleted

Custom SqlKata Queries

SqlKata supports a lot of custom query operations, many of which are not supported by SqlHydra query builders. The kata custom operation allows you to manipulate the underlying SqlKata query directly. For example, you could use this to conditionally add columns to the WHERE or ORDER BY clauses:

let getCustomers filters = 
  select {
      for c in main.Customer do
      where (c.FirstName = "John")
      kata (fun query -> 
          match filters.LastName with
          | Some lastName -> query.Where("c.LastName", lastName)
          | None -> query
      )
      kata (fun query -> 
          query.OrderBy(filters.SortColumns)
      )
  }

Custom SQL Queries

Sometimes it is easier to just write a custom SQL query. This can be helpful when you have a very custom query, or are using SQL constructs that do not yet exist in SqlHydra.Query. You can do this while still maintaining the benefits of the strongly typed generated HydraReader.

This example uses the generated HydraReader to hydrate the generated dbo.Product table record.

let getTop10Products(conn: SqlConnection) = task {
    let sql = $"SELECT TOP 10 * FROM {nameof dbo.Product} p"
    use cmd = new SqlCommand(sql, conn)
    use! reader = cmd.ExecuteReaderAsync()
    let hydra = HydraReader(reader)

    return [
        while reader.Read() do
            hydra.``dbo.Product``.Read()
    ]
}

The next example uses a query expression that modifies the underlying SqlKata query (using the the kata custom operation) to override the SELECT clause, and then manually reads the results into a custom record type. This technique can be useful if you want to select custom columns that use functions with a custom result type, but you still want to use a strongly typed query expression. 

/// A custom result type to be used for this query.
type CityRow = { City3: string; Number: int }

let getCities() = task {
    use ctx = openContext()

    let! reader =
        select {
            for a in Person.Address do
            where (a.City |=| [ "Seattle"; "Denver" ])
            kata (fun query -> query.SelectRaw("SUBSTRING(City, 1, 3) AS City3, 123 AS Number"))
        }
        |> ctx.GetReaderAsync

    return
        [
            while reader.Read() do
                {
                    City3 = reader.Get "City3"
                    Number = reader.Get "Number"
                }
        ]
}

See more examples of using the generated HydraReader: https://github.com/JordanMarr/SqlHydra/wiki/DataReaders