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hazzikhazzik
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Implement Connection.GetSchema (#185)
* WIP Connection.GetSchema * Code cleanup * Implement ReservedWords * Ooops * Fix tests * Add test for ArgumentOutOfRangeException * Refactoring * Use DbMetaDataCollectionNames && DbMetaDataColumnNames where possible * Remove redundant code * Implement Columns schema * Add Columns schema metadata * Add ForeignKeys schema * Implement Indexes metadata * Fix indexes test * Use constant * Extract restrictions arrays
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‎DuckDB.NET.Data/DuckDBConnection.cs‎

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@@ -215,4 +215,13 @@ public DuckDBConnection Duplicate()
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return duplicatedConnection;
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}
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public override DataTable GetSchema() =>
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GetSchema(DbMetaDataCollectionNames.MetaDataCollections);
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public override DataTable GetSchema(string collectionName) =>
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GetSchema(collectionName, null);
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public override DataTable GetSchema(string collectionName, string?[]? restrictionValues) =>
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DuckDBSchema.GetSchema(this, collectionName, restrictionValues);
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}

‎DuckDB.NET.Data/DuckDBSchema.cs‎

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using System;
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using System.Data;
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using System.Data.Common;
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using System.Linq;
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using System.Text;
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namespace DuckDB.NET.Data;
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internal static class DuckDBSchema
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{
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private static readonly string[] TableRestrictions =
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["table_catalog", "table_schema", "table_name", "table_type"];
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private static readonly string[] ColumnRestrictions =
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["table_catalog", "table_schema", "table_name", "column_name"];
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private static readonly string[] ForeignKeyRestrictions =
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["constraint_catalog", "constraint_schema", "table_name", "constraint_name"];
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private static readonly string[] IndexesRestrictions =
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["index_catalog", "index_schema", "table_name", "index_name"];
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public static DataTable GetSchema(DuckDBConnection connection, string collectionName, string?[]? restrictionValues) =>
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collectionName.ToUpperInvariant() switch
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{
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"METADATACOLLECTIONS" => GetMetaDataCollections(),
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"RESTRICTIONS" => GetRestrictions(),
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"RESERVEDWORDS" => GetReservedWords(connection),
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"TABLES" => GetTables(connection, restrictionValues),
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"COLUMNS" => GetColumns(connection, restrictionValues),
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"FOREIGNKEYS" => GetForeignKeys(connection, restrictionValues),
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"INDEXES" => GetIndexes(connection, restrictionValues),
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_ => throw new ArgumentOutOfRangeException(nameof(collectionName), collectionName, "Invalid collection name.")
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};
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private static DataTable GetMetaDataCollections() =>
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new(DbMetaDataCollectionNames.MetaDataCollections)
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{
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Columns =
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{
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{ DbMetaDataColumnNames.CollectionName, typeof(string) },
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{ DbMetaDataColumnNames.NumberOfRestrictions, typeof(int) },
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{ DbMetaDataColumnNames.NumberOfIdentifierParts, typeof(int) }
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},
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Rows =
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{
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{ DbMetaDataCollectionNames.MetaDataCollections, 0, 0 },
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{ DbMetaDataCollectionNames.Restrictions, 0, 0 },
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{ DbMetaDataCollectionNames.ReservedWords, 0, 0 },
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{ DuckDbMetaDataCollectionNames.Tables, TableRestrictions.Length, 3 },
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{ DuckDbMetaDataCollectionNames.Columns, ColumnRestrictions.Length, 4 },
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{ DuckDbMetaDataCollectionNames.ForeignKeys, ForeignKeyRestrictions.Length, 3 },
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{ DuckDbMetaDataCollectionNames.Indexes, IndexesRestrictions.Length, 3 },
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}
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};
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private static DataTable GetRestrictions() =>
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new(DbMetaDataCollectionNames.Restrictions)
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{
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Columns =
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{
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{ "CollectionName", typeof(string) },
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{ "RestrictionName", typeof(string) },
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{ "RestrictionDefault", typeof(string) },
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{ "RestrictionNumber", typeof(int) }
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},
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Rows =
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{
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{ DuckDbMetaDataCollectionNames.Tables, "Catalog", "table_catalog", 1 },
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{ DuckDbMetaDataCollectionNames.Tables, "Schema", "table_schema", 2 },
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{ DuckDbMetaDataCollectionNames.Tables, "Table", "table_name", 3 },
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{ DuckDbMetaDataCollectionNames.Tables, "TableType", "table_type", 4 },
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{ DuckDbMetaDataCollectionNames.Columns, "Catalog", "table_catalog", 1 },
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{ DuckDbMetaDataCollectionNames.Columns, "Schema", "table_schema", 2 },
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{ DuckDbMetaDataCollectionNames.Columns, "Table", "table_name", 3 },
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{ DuckDbMetaDataCollectionNames.Columns, "Column", "column_name", 4 },
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{ DuckDbMetaDataCollectionNames.ForeignKeys, "Catalog", "constraint_catalog", 1 },
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{ DuckDbMetaDataCollectionNames.ForeignKeys, "Schema", "constraint_schema", 2 },
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{ DuckDbMetaDataCollectionNames.ForeignKeys, "Table", "table_name", 3 },
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{ DuckDbMetaDataCollectionNames.ForeignKeys, "Constraint", "constraint_name", 4 },
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{ DuckDbMetaDataCollectionNames.Indexes, "Catalog", "constraint_catalog", 1 },
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{ DuckDbMetaDataCollectionNames.Indexes, "Schema", "constraint_schema", 2 },
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{ DuckDbMetaDataCollectionNames.Indexes, "Table", "table_name", 3 },
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{ DuckDbMetaDataCollectionNames.Indexes, "Constraint", "constraint_name", 4 },
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},
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};
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private static DataTable GetReservedWords(DuckDBConnection connection)
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{
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using var command = connection.CreateCommand();
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command.CommandText = "SELECT keyword_name as ReservedWord FROM duckdb_keywords() WHERE keyword_category = 'reserved'";
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command.CommandType = CommandType.Text;
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return GetDataTable(DbMetaDataCollectionNames.ReservedWords, command);
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}
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private static DataTable GetTables(DuckDBConnection connection, string?[]? restrictionValues)
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{
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if (restrictionValues?.Length > TableRestrictions.Length)
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throw new ArgumentException("Too many restrictions", nameof(restrictionValues));
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const string query = "SELECT table_catalog, table_schema, table_name, table_type FROM information_schema.tables";
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using var command = BuildCommand(connection, query, restrictionValues, true, TableRestrictions);
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return GetDataTable(DuckDbMetaDataCollectionNames.Tables, command);
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}
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private static DataTable GetColumns(DuckDBConnection connection, string?[]? restrictionValues)
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{
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if (restrictionValues?.Length > ColumnRestrictions.Length)
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throw new ArgumentException("Too many restrictions", nameof(restrictionValues));
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const string query =
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"""
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SELECT
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table_catalog, table_schema, table_name, column_name,
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ordinal_position, column_default, is_nullable, data_type,
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character_maximum_length, character_octet_length,
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numeric_precision, numeric_precision_radix,
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numeric_scale, datetime_precision,
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character_set_catalog, character_set_schema, character_set_name, collation_catalog
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FROM information_schema.columns
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""";
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using var command = BuildCommand(connection, query, restrictionValues, true, ColumnRestrictions);
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return GetDataTable(DuckDbMetaDataCollectionNames.Columns, command);
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}
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private static DataTable GetForeignKeys(DuckDBConnection connection, string?[]? restrictionValues)
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{
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if (restrictionValues?.Length > ForeignKeyRestrictions.Length)
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throw new ArgumentException("Too many restrictions", nameof(restrictionValues));
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const string query =
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"""
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SELECT
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constraint_catalog, constraint_schema, constraint_name,
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table_catalog, table_schema, table_name, constraint_type,
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is_deferrable, initially_deferred
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FROM information_schema.table_constraints
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WHERE constraint_type = 'FOREIGN KEY'
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""";
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using var command = BuildCommand(connection, query, restrictionValues, false, ForeignKeyRestrictions);
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return GetDataTable(DuckDbMetaDataCollectionNames.ForeignKeys, command);
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}
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private static DataTable GetIndexes(DuckDBConnection connection, string?[]? restrictionValues)
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{
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if (restrictionValues?.Length > IndexesRestrictions.Length)
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throw new ArgumentException("Too many restrictions", nameof(restrictionValues));
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const string query =
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"""
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SELECT
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database_name as index_catalog,
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schema_name as index_schema,
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index_name,
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table_name,
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is_unique,
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is_primary
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FROM duckdb_indexes()
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""";
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using var command = BuildCommand(connection, query, restrictionValues, true, IndexesRestrictions);
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return GetDataTable(DuckDbMetaDataCollectionNames.Indexes, command);
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}
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private static DuckDBCommand BuildCommand(DuckDBConnection connection, string query, string?[]? restrictions,
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bool addWhere, string[]? restrictionNames)
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{
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var command = connection.CreateCommand();
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if (restrictions is not { Length: > 0 } || restrictionNames == null)
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{
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command.CommandText = query;
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return command;
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}
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var builder = new StringBuilder(query);
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foreach (var (name, restriction) in restrictionNames.Zip(restrictions, Tuple.Create))
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{
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if (restriction?.Length > 0)
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{
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if (addWhere)
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{
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builder.Append(" WHERE ");
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addWhere = false;
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}
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else
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{
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builder.Append(" AND ");
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}
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builder.Append($"{name} = ${name}");
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command.Parameters.Add(new DuckDBParameter(name, restriction));
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}
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}
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command.CommandText = builder.ToString();
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return command;
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}
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private static DataTable GetDataTable(string tableName, DuckDBCommand command)
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{
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var table = new DataTable(tableName);
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try
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{
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using var reader = command.ExecuteReader();
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table.BeginLoadData();
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table.Load(reader);
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}
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finally
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{
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table.EndLoadData();
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}
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return table;
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}
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}

‎DuckDB.NET.Data/DuckDbMetaDataCollectionNames.cs‎

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namespace DuckDB.NET.Data;
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internal static class DuckDbMetaDataCollectionNames
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{
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public const string Tables = "Tables";
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public const string Columns = "Columns";
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public const string ForeignKeys = "ForeignKeys";
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public const string Indexes = "Indexes";
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}

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